diff --git a/doc/source/whatsnew/v1.2.0.rst b/doc/source/whatsnew/v1.2.0.rst
index 812af544ed9d8..312a850ec3fd1 100644
--- a/doc/source/whatsnew/v1.2.0.rst
+++ b/doc/source/whatsnew/v1.2.0.rst
@@ -439,6 +439,7 @@ Indexing
 - Bug in :meth:`DataFrame.__getitem__` and :meth:`DataFrame.loc.__getitem__` with :class:`IntervalIndex` columns and a numeric indexer (:issue:`26490`)
 - Bug in :meth:`Series.loc.__getitem__` with a non-unique :class:`MultiIndex` and an empty-list indexer (:issue:`13691`)
 - Bug in indexing on a :class:`Series` or :class:`DataFrame` with a :class:`MultiIndex` with a level named "0" (:issue:`37194`)
+- Bug in :meth:`Series.__getitem__` when using an unsigned integer array as an indexer giving incorrect results or segfaulting instead of raising ``KeyError`` (:issue:`37218`)
 
 Missing
 ^^^^^^^
diff --git a/pandas/core/indexes/range.py b/pandas/core/indexes/range.py
index 74ec892d5f8a0..3afcb0fa343d5 100644
--- a/pandas/core/indexes/range.py
+++ b/pandas/core/indexes/range.py
@@ -17,9 +17,9 @@
     ensure_python_int,
     is_float,
     is_integer,
-    is_integer_dtype,
     is_list_like,
     is_scalar,
+    is_signed_integer_dtype,
     is_timedelta64_dtype,
 )
 from pandas.core.dtypes.generic import ABCTimedeltaIndex
@@ -369,7 +369,7 @@ def get_indexer(self, target, method=None, limit=None, tolerance=None):
             start, stop, step = reverse.start, reverse.stop, reverse.step
 
         target_array = np.asarray(target)
-        if not (is_integer_dtype(target_array) and target_array.ndim == 1):
+        if not (is_signed_integer_dtype(target_array) and target_array.ndim == 1):
             # checks/conversions/roundings are delegated to general method
             return super().get_indexer(target, method=method, tolerance=tolerance)
 
diff --git a/pandas/tests/series/indexing/test_getitem.py b/pandas/tests/series/indexing/test_getitem.py
index 9f6aab823c3ad..ab34423fa7acd 100644
--- a/pandas/tests/series/indexing/test_getitem.py
+++ b/pandas/tests/series/indexing/test_getitem.py
@@ -147,6 +147,16 @@ def test_getitem_intlist_multiindex_numeric_level(self, dtype, box):
         with pytest.raises(KeyError, match="5"):
             ser[key]
 
+    def test_getitem_uint_array_key(self, uint_dtype):
+        # GH #37218
+        ser = Series([1, 2, 3])
+        key = np.array([4], dtype=uint_dtype)
+
+        with pytest.raises(KeyError, match="4"):
+            ser[key]
+        with pytest.raises(KeyError, match="4"):
+            ser.loc[key]
+
 
 class TestGetitemBooleanMask:
     def test_getitem_boolean(self, string_series):