diff --git a/tests/test_labelarray.py b/tests/test_labelarray.py
index 64004fe9..c08a58e4 100644
--- a/tests/test_labelarray.py
+++ b/tests/test_labelarray.py
@@ -1,10 +1,13 @@
 from itertools import product
 from operator import eq, ne
-import numpy as np
 import warnings
 
+import numpy as np
+from toolz import take
+
 from zipline.lib.labelarray import LabelArray
 from zipline.testing import check_arrays, parameter_space, ZiplineTestCase
+from zipline.testing.predicates import assert_equal
 from zipline.utils.compat import unicode
 
 
@@ -337,3 +340,85 @@ class LabelArrayTestCase(ZiplineTestCase):
         # Write the whole array.
         arr[:] = orig_arr
         check_arrays(arr, orig_arr)
+
+    def test_narrow_code_storage(self):
+        def check_roundtrip(arr):
+            assert_equal(
+                arr.as_string_array(),
+                LabelArray(
+                    arr.as_string_array(),
+                    arr.missing_value,
+                ).as_string_array(),
+            )
+
+        def create_categories(width, plus_one):
+            length = int(width / 8) + plus_one
+            return [
+                ''.join(cs)
+                for cs in take(
+                    2 ** width + plus_one,
+                    product([chr(c) for c in range(256)], repeat=length),
+                )
+            ]
+
+        # uint8
+        categories = create_categories(8, plus_one=False)
+        arr = LabelArray(
+            [],
+            missing_value=categories[0],
+            categories=categories,
+        )
+        self.assertEqual(arr.itemsize, 1)
+        check_roundtrip(arr)
+
+        # uint8 inference
+        arr = LabelArray(categories, missing_value=categories[0])
+        self.assertEqual(arr.itemsize, 1)
+        check_roundtrip(arr)
+
+        # just over uint8
+        categories = create_categories(8, plus_one=True)
+        arr = LabelArray(
+            [],
+            missing_value=categories[0],
+            categories=categories,
+        )
+        self.assertEqual(arr.itemsize, 2)
+        check_roundtrip(arr)
+
+        # uint16 inference
+        arr = LabelArray(categories, missing_value=categories[0])
+        self.assertEqual(arr.itemsize, 2)
+        check_roundtrip(arr)
+
+        # fits in uint16
+        categories = create_categories(16, plus_one=False)
+        arr = LabelArray(
+            [], missing_value=categories[0],
+            categories=categories,
+        )
+        self.assertEqual(arr.itemsize, 2)
+        check_roundtrip(arr)
+
+        # uint16 inference
+        arr = LabelArray(categories, missing_value=categories[0])
+        self.assertEqual(arr.itemsize, 2)
+        check_roundtrip(arr)
+
+        # just over uint16
+        categories = create_categories(16, plus_one=True)
+        arr = LabelArray(
+            [],
+            missing_value=categories[0],
+            categories=categories,
+        )
+        self.assertEqual(arr.itemsize, 4)
+        check_roundtrip(arr)
+
+        # uint32 inference
+        arr = LabelArray(categories, missing_value=categories[0])
+        self.assertEqual(arr.itemsize, 4)
+        check_roundtrip(arr)
+
+        # NOTE: we could do this for 32 and 64; however, no one has enough RAM
+        # or time for that.
diff --git a/zipline/lib/_factorize.pyx b/zipline/lib/_factorize.pyx
index 31cd0ff2..a90cec9f 100644
--- a/zipline/lib/_factorize.pyx
+++ b/zipline/lib/_factorize.pyx
@@ -1,53 +1,150 @@
 """
 Factorization algorithms.
 """
-from numpy cimport ndarray, int64_t, PyArray_Check, import_array
-from numpy import arange, asarray, empty, int64, isnan, ndarray, zeros
+from libc.math cimport floor, log
+cimport numpy as np
+import numpy as np
 
-import_array()
+from zipline.utils.numpy_utils import unsigned_int_dtype_with_size_in_bytes
+
+np.import_array()
 
 
-cpdef factorize_strings_known_categories(ndarray[object] values,
-                                         list categories,
-                                         object missing_value,
-                                         int sort):
-    """
-    Factorize an array whose categories are already known.
+cdef inline double log2(double d):
+    return log(d) / log(2);
 
-    Any entries not in the specified categories will be given the code for
-    `missing_value`.
-    """
+
+ctypedef fused unsigned_integral:
+    np.uint8_t
+    np.uint16_t
+    np.uint32_t
+    np.uint64_t
+
+
+cdef factorize_strings_known_impl(np.ndarray[object] values,
+                                  Py_ssize_t nvalues,
+                                  list categories,
+                                  object missing_value,
+                                  bint sort,
+                                  np.ndarray[unsigned_integral] codes):
     if missing_value not in categories:
         categories.insert(0, missing_value)
 
     if sort:
         categories = sorted(categories)
 
-    cdef:
-        Py_ssize_t      nvalues = len(values)
-        dict reverse_categories = dict(
-            zip(categories, range(len(categories)))
-        )
-
-    if not nvalues:
-        return (
-            asarray([], dtype=int64),
-            asarray(categories, dtype=object),
-            reverse_categories,
-        )
-
-    cdef:
-        Py_ssize_t            i
-        Py_ssize_t missing_code = reverse_categories[missing_value]
-        ndarray[int64_t]  codes = empty(nvalues, dtype=int64)
+    cdef dict reverse_categories = dict(
+        zip(categories, range(len(categories)))
+    )
+    cdef Py_ssize_t i
+    cdef Py_ssize_t missing_code = reverse_categories[missing_value]
 
     for i in range(nvalues):
         codes[i] = reverse_categories.get(values[i], missing_code)
 
-    return codes, asarray(categories, dtype=object), reverse_categories
+    return codes, np.asarray(categories, dtype=object), reverse_categories
 
 
-cpdef factorize_strings(ndarray[object] values,
+cpdef factorize_strings_known_categories(np.ndarray[object] values,
+                                         list categories,
+                                         object missing_value,
+                                         bint sort):
+    """
+    Factorize an array whose categories are already known.
+
+    Any entries not in the specified categories will be given the code for
+    `missing_value`.
+    """
+    cdef Py_ssize_t ncategories = len(categories)
+    cdef Py_ssize_t nvalues = len(values)
+    if ncategories <= 2 ** 8:
+        return factorize_strings_known_impl[np.uint8_t](
+            values,
+            nvalues,
+            categories,
+            missing_value,
+            sort,
+            np.empty(nvalues, dtype=np.uint8)
+        )
+    elif ncategories <= 2 ** 16:
+        return factorize_strings_known_impl[np.uint16_t](
+            values,
+            nvalues,
+            categories,
+            missing_value,
+            sort,
+            np.empty(nvalues, np.uint16),
+        )
+    elif ncategories <= 2 ** 32:
+        return factorize_strings_known_impl[np.uint32_t](
+            values,
+            nvalues,
+            categories,
+            missing_value,
+            sort,
+            np.empty(nvalues, np.uint32),
+        )
+    elif ncategories <= 2 ** 64:
+        return factorize_strings_known_impl[np.uint64_t](
+            values,
+            nvalues,
+            categories,
+            missing_value,
+            sort,
+            np.empty(nvalues, np.uint64),
+        )
+    else:
+        raise ValueError('ncategories larger than uint64')
+
+
+cdef factorize_strings_impl(np.ndarray[object] values,
+                            Py_ssize_t nvalues,
+                            object missing_value,
+                            bint sort,
+                            np.ndarray[unsigned_integral] codes):
+    cdef list categories = [missing_value]
+    cdef dict reverse_categories = {missing_value: 0}
+
+    cdef Py_ssize_t i, code
+    cdef object key = None
+
+    for i in range(nvalues):
+        key = values[i]
+        code = reverse_categories.get(key, -1)
+        if code == -1:
+            # Assign new code.
+            code = len(reverse_categories)
+            reverse_categories[key] = code
+            categories.append(key)
+        codes[i] = code
+
+    cdef np.ndarray[np.int64_t, ndim=1] sorter
+    cdef np.ndarray[unsigned_integral, ndim=1] reverse_indexer
+    cdef int ncategories
+    cdef np.ndarray[object] categories_array = np.asarray(
+        categories,
+        dtype=object,
+    )
+
+    if sort:
+        # This is all adapted from pandas.core.algorithms.factorize.
+        ncategories = len(categories_array)
+        sorter = np.zeros(ncategories, dtype=np.int64)
+
+        # Don't include missing_value in the argsort, because None is
+        # unorderable with bytes/str in py3. Always just sort it to 0.
+        sorter[1:] = categories_array[1:].argsort() + 1
+        reverse_indexer = np.empty(ncategories, dtype=codes.dtype)
+        reverse_indexer.put(sorter, np.arange(ncategories))
+
+        codes = reverse_indexer.take(codes)
+        categories_array = categories_array.take(sorter)
+        reverse_categories = dict(zip(categories_array, range(ncategories)))
+
+    return codes, categories_array, reverse_categories
+
+
+cpdef factorize_strings(np.ndarray[object] values,
                         object missing_value,
                         int sort):
     """
@@ -63,52 +160,60 @@ cpdef factorize_strings(ndarray[object] values,
     ObjectVector.  Python's builtin data structures are **really**
     well-optimized.)
     """
-    cdef:
-        Py_ssize_t      nvalues = len(values)
-        list         categories = [missing_value]
-        dict reverse_categories = {missing_value: 0}
+    cdef Py_ssize_t nvalues = len(values)
+    cdef np.ndarray codes
+    cdef np.ndarray categories_array
+    cdef dict reverse_categories
 
-    # Short circuit on empty array.
-    if not nvalues:
-        return (
-            asarray([], dtype=int64),
-            asarray(categories, dtype=object),
-            reverse_categories,
+    if nvalues <= 2 ** 8:
+        # we won't try to shrink because the ``codes`` array cannot get any
+        # smaller
+        return factorize_strings_impl[np.uint8_t](
+            values,
+            nvalues,
+            missing_value,
+            sort,
+            np.empty(nvalues, dtype=np.uint8)
         )
+    elif nvalues <= 2 ** 16:
+        (codes,
+         categories_array,
+         reverse_categories) = factorize_strings_impl[np.uint16_t](
+            values,
+            nvalues,
+            missing_value,
+            sort,
+            np.empty(nvalues, np.uint16),
+        )
+    elif nvalues <= 2 ** 32:
+        (codes,
+         categories_array,
+         reverse_categories) = factorize_strings_impl[np.uint32_t](
+            values,
+            nvalues,
+            missing_value,
+            sort,
+            np.empty(nvalues, np.uint32),
+        )
+    elif nvalues <= 2 ** 64:
+        (codes,
+         categories_array,
+         reverse_categories) = factorize_strings_impl[np.uint64_t](
+            values,
+            nvalues,
+            missing_value,
+            sort,
+            np.empty(nvalues, np.uint64),
+        )
+    else:
+        # unreachable
+        raise ValueError('nvalues larger than uint64')
 
-    cdef:
-        Py_ssize_t      i, code
-        object              key = None
-        ndarray[int64_t]  codes = empty(nvalues, dtype=int64)
-
-    for i in range(nvalues):
-        key = values[i]
-        code = reverse_categories.get(key, -1)
-        if code == -1:
-            # Assign new code.
-            code = len(reverse_categories)
-            reverse_categories[key] = code
-            categories.append(key)
-        codes[i] = code
-
-    cdef ndarray[int64_t, ndim=1] sorter
-    cdef ndarray[int64_t, ndim=1] reverse_indexer
-    cdef int ncategories
-    cdef ndarray[object] categories_array = asarray(categories, dtype=object)
-
-    if sort:
-        # This is all adapted from pandas.core.algorithms.factorize.
-        ncategories = len(categories_array)
-        sorter = zeros(ncategories, dtype=int64)
-
-        # Don't include missing_value in the argsort, because None is
-        # unorderable with bytes/str in py3. Always just sort it to 0.
-        sorter[1:] = categories_array[1:].argsort() + 1
-        reverse_indexer = empty(ncategories, dtype=int64)
-        reverse_indexer.put(sorter, arange(ncategories))
-
-        codes = reverse_indexer.take(codes)
-        categories_array = categories_array.take(sorter)
-        reverse_categories = dict(zip(categories_array, range(ncategories)))
+    if len(categories_array) < 2 ** codes.dtype.itemsize:
+        # if there are a lot of duplicates in the values we may need to shrink
+        # the width of the ``codes`` array
+        codes = codes.astype(unsigned_int_dtype_with_size_in_bytes(
+            floor(log2(len(categories_array))),
+        ))
 
     return codes, categories_array, reverse_categories
diff --git a/zipline/lib/labelarray.py b/zipline/lib/labelarray.py
index 1a469b43..c9db21e6 100644
--- a/zipline/lib/labelarray.py
+++ b/zipline/lib/labelarray.py
@@ -21,7 +21,7 @@ from zipline.utils.input_validation import (
 )
 from zipline.utils.numpy_utils import (
     bool_dtype,
-    int_dtype_with_size_in_bytes,
+    unsigned_int_dtype_with_size_in_bytes,
     is_object,
 )
 from zipline.utils.pandas_utils import ignore_pandas_nan_categorical_warning
@@ -81,6 +81,7 @@ class CategoryMismatch(ValueError):
             )
         )
 
+
 _NotPassed = sentinel('_NotPassed')
 
 
@@ -175,7 +176,7 @@ class LabelArray(ndarray):
             )
         categories.setflags(write=False)
 
-        return cls._from_codes_and_metadata(
+        return cls.from_codes_and_metadata(
             codes=codes.reshape(values.shape),
             categories=categories,
             reverse_categories=reverse_categories,
@@ -183,13 +184,24 @@ class LabelArray(ndarray):
         )
 
     @classmethod
-    def _from_codes_and_metadata(cls,
-                                 codes,
-                                 categories,
-                                 reverse_categories,
-                                 missing_value):
+    def from_codes_and_metadata(cls,
+                                codes,
+                                categories,
+                                reverse_categories,
+                                missing_value):
         """
-        View codes as a LabelArray and set LabelArray metadata on the result.
+        Rehydrate a LabelArray from the codes and metadata.
+
+        Parameters
+        ----------
+        codes : np.ndarray[integral]
+            The codes for the label array.
+        categories : np.ndarray[object]
+            The unique string categories.
+        reverse_categories : dict[str, int]
+            The mapping from category to its code-index.
+        missing_value : any
+            The value used to represent missing data.
         """
         ret = codes.view(type=cls, dtype=np.void)
         ret._categories = categories
@@ -289,7 +301,7 @@ class LabelArray(ndarray):
         """
         return self.view(
             type=ndarray,
-            dtype=int_dtype_with_size_in_bytes(self.itemsize),
+            dtype=unsigned_int_dtype_with_size_in_bytes(self.itemsize),
         )
 
     def as_string_array(self):
@@ -384,7 +396,9 @@ class LabelArray(ndarray):
 
         # Result is a scalar value, which will be an instance of np.void.
         # Map it back to one of our category entries.
-        index = result.view(int_dtype_with_size_in_bytes(self.itemsize))
+        index = result.view(
+            unsigned_int_dtype_with_size_in_bytes(self.itemsize),
+        )
         return self.categories[index]
 
     def is_missing(self):
@@ -514,11 +528,11 @@ class LabelArray(ndarray):
         Make an empty LabelArray with the same categories as ``self``, filled
         with ``self.missing_value``.
         """
-        return type(self)._from_codes_and_metadata(
+        return type(self).from_codes_and_metadata(
             codes=np.full(
                 shape,
                 self.reverse_categories[self.missing_value],
-                dtype=int_dtype_with_size_in_bytes(self.itemsize),
+                dtype=unsigned_int_dtype_with_size_in_bytes(self.itemsize),
             ),
             categories=self.categories,
             reverse_categories=self.reverse_categories,
diff --git a/zipline/utils/numpy_utils.py b/zipline/utils/numpy_utils.py
index 0a13b08f..9011df6c 100644
--- a/zipline/utils/numpy_utils.py
+++ b/zipline/utils/numpy_utils.py
@@ -87,6 +87,13 @@ INT_DTYPES_BY_SIZE_BYTES = OrderedDict([
     (8, dtype('int64')),
 ])
 
+UNSIGNED_INT_DTYPES_BY_SIZE_BYTES = OrderedDict([
+    (1, dtype('uint8')),
+    (2, dtype('uint16')),
+    (4, dtype('uint32')),
+    (8, dtype('uint64')),
+])
+
 
 def int_dtype_with_size_in_bytes(size):
     try:
@@ -95,6 +102,15 @@ def int_dtype_with_size_in_bytes(size):
         raise ValueError("No integral dtype whose size is %d bytes." % size)
 
 
+def unsigned_int_dtype_with_size_in_bytes(size):
+    try:
+        return UNSIGNED_INT_DTYPES_BY_SIZE_BYTES[size]
+    except KeyError:
+        raise ValueError(
+            "No unsigned integral dtype whose size is %d bytes." % size
+        )
+
+
 class NoDefaultMissingValue(Exception):
     pass