diff -r d07d0afea9a7 Doc/library/zlib.rst
--- a/Doc/library/zlib.rst	Mon Jun 13 16:19:06 2011 +0200
+++ b/Doc/library/zlib.rst	Mon Jun 13 20:29:27 2011 +0200
@@ -213,6 +213,13 @@
    seeks into the stream at a future point.
 
 
+.. data:: ZLIB_RUNTIME_VERSION
+
+   The version string of the zlib library actually loaded by the interpreter.
+
+   .. versionadded:: 3.3
+
+
 .. seealso::
 
    Module :mod:`gzip`
diff -r d07d0afea9a7 Lib/test/test_zlib.py
--- a/Lib/test/test_zlib.py	Mon Jun 13 16:19:06 2011 +0200
+++ b/Lib/test/test_zlib.py	Mon Jun 13 20:29:27 2011 +0200
@@ -13,6 +13,16 @@
     mmap = None
 
 
+class VersionTestCase(unittest.TestCase):
+
+    def test_library_version(self):
+        # On the build system, ZLIB_RUNTIME_VERSION and ZLIB_VERSION should match.
+        # ZLIB_RUNTIME_VERSION is the actual library version while ZLIB_VERSION is
+        # the version from the header file. On the build system, the headers
+        # should match with the library exactly. At runtime, only the first
+        # digit is required to match.
+        self.assertEqual(zlib.ZLIB_RUNTIME_VERSION, zlib.ZLIB_VERSION)
+
 class ChecksumTestCase(unittest.TestCase):
     # checksum test cases
     def test_crc32start(self):
@@ -627,6 +637,7 @@
 
 def test_main():
     support.run_unittest(
+        VersionTestCase,
         ChecksumTestCase,
         ChecksumBigBufferTestCase,
         ExceptionTestCase,
diff -r d07d0afea9a7 Modules/zlibmodule.c
--- a/Modules/zlibmodule.c	Mon Jun 13 16:19:06 2011 +0200
+++ b/Modules/zlibmodule.c	Mon Jun 13 20:29:27 2011 +0200
@@ -1158,6 +1158,10 @@
     if (ver != NULL)
         PyModule_AddObject(m, "ZLIB_VERSION", ver);
 
+    ver = PyUnicode_FromString(zlibVersion());
+    if (ver != NULL)
+        PyModule_AddObject(m, "ZLIB_RUNTIME_VERSION", ver);
+
     PyModule_AddStringConstant(m, "__version__", "1.0");
 
     return m;