diff --git a/doc/source/whatsnew/v0.22.0.txt b/doc/source/whatsnew/v0.22.0.txt
index 09b504cac5ed4..fd161e91ab37c 100644
--- a/doc/source/whatsnew/v0.22.0.txt
+++ b/doc/source/whatsnew/v0.22.0.txt
@@ -245,4 +245,5 @@ Other
 - Fixed a bug where creating a Series from an array that contains both tz-naive and tz-aware values will result in a Series whose dtype is tz-aware instead of object (:issue:`16406`)
 - Fixed construction of a :class:`Series` from a ``dict`` containing ``NaN`` as key (:issue:`18480`)
 - Adding a ``Period`` object to a ``datetime`` or ``Timestamp`` object will now correctly raise a ``TypeError`` (:issue:`17983`)
--
+- BLD: since we already use setuptools, let's remove the optional logic in setup.py (:issue:`18113`)
+- 
diff --git a/setup.py b/setup.py
index 68e1319458a33..22c2ef4c7509b 100755
--- a/setup.py
+++ b/setup.py
@@ -9,9 +9,11 @@
 import os
 from os.path import join as pjoin
 
+import pkg_resources
 import sys
 import shutil
 from distutils.version import LooseVersion
+from setuptools import setup, Command
 
 # versioning
 import versioneer
@@ -38,14 +40,6 @@ def is_platform_mac():
 except ImportError:
     _CYTHON_INSTALLED = False
 
-try:
-    import pkg_resources
-    from setuptools import setup, Command
-    _have_setuptools = True
-except ImportError:
-    # no setuptools installed
-    from distutils.core import setup, Command
-    _have_setuptools = False
 
 setuptools_kwargs = {}
 min_numpy_ver = '1.9.0'
@@ -56,10 +50,6 @@ def is_platform_mac():
                                               'pytz >= 2011k',
                                               'numpy >= %s' % min_numpy_ver],
                          'setup_requires': ['numpy >= %s' % min_numpy_ver]}
-    if not _have_setuptools:
-        sys.exit("need setuptools/distribute for Py3k"
-                 "\n$ pip install distribute")
-
 else:
     setuptools_kwargs = {
         'install_requires': ['python-dateutil',
@@ -69,16 +59,6 @@ def is_platform_mac():
         'zip_safe': False,
     }
 
-    if not _have_setuptools:
-        try:
-            import numpy  # noqa:F401
-            import dateutil  # noqa:F401
-            setuptools_kwargs = {}
-        except ImportError:
-            sys.exit("install requires: 'python-dateutil < 2','numpy'."
-                     "  use pip or easy_install."
-                     "\n   $ pip install 'python-dateutil < 2' 'numpy'")
-
 from distutils.extension import Extension  # noqa:E402
 from distutils.command.build import build  # noqa:E402
 from distutils.command.build_ext import build_ext as _build_ext  # noqa:E402
@@ -695,7 +675,7 @@ def pxd(name):
 # ----------------------------------------------------------------------
 # ujson
 
-if suffix == '.pyx' and 'setuptools' in sys.modules:
+if suffix == '.pyx':
     # undo dumb setuptools bug clobbering .pyx sources back to .c
     for ext in extensions:
         if ext.sources[0].endswith(('.c', '.cpp')):
@@ -729,9 +709,7 @@ def pxd(name):
                       sources=['pandas/util/move.c'])
 extensions.append(_move_ext)
 
-
-if _have_setuptools:
-    setuptools_kwargs["test_suite"] = "nose.collector"
+setuptools_kwargs["test_suite"] = "nose.collector"
 
 # The build cache system does string matching below this point.
 # if you change something, be careful.