Index: src/zc/buildout/tests.py
===================================================================
--- src/zc/buildout/tests.py	(revision 123353)
+++ src/zc/buildout/tests.py	(working copy)
@@ -1309,6 +1309,103 @@
 
     """
 
+def recipe_extras():
+    """
+
+The buildout will check for extra requirements of recipes.
+
+Let's create a recipe egg
+
+    >>> mkdir('recipe')
+    >>> write('recipe', 'recipe.py',
+    ... '''
+    ... class Recipe:
+    ...     def __init__(*a): pass
+    ...     def install(self):
+    ...         return ()
+    ...     update = install
+    ... ''')
+
+    >>> write('recipe', 'setup.py',
+    ... '''
+    ... from setuptools import setup
+    ... setup(name='recipe', version='1', py_modules=['recipe'],
+    ...       entry_points={'zc.buildout': ['default = recipe:Recipe',
+    ...                                     'ext = recipe:Recipe [extra]'],},
+    ...       extras_require={'extra': ['extra']}
+    ...       )
+    ... ''')
+
+    >>> write('recipe', 'README', '')
+
+    >>> print system(buildout+' setup recipe bdist_egg'), # doctest: +ELLIPSIS
+    Running setup script 'recipe/setup.py'.
+    ...
+
+    >>> rmdir('recipe', 'build')
+
+And an optional extra requirement
+
+    >>> mkdir('extra')
+    >>> write('extra', 'recipe.py',
+    ... '''
+    ... class Dummy:
+    ...     pass
+    ... ''')
+
+    >>> write('extra', 'setup.py',
+    ... '''
+    ... from setuptools import setup
+    ... setup(name='extra', version='1', py_modules=['recipe'],
+    ...       )
+    ... ''')
+
+    >>> write('extra', 'README', '')
+
+    >>> print system(buildout+' setup extra bdist_egg'), # doctest: +ELLIPSIS
+    Running setup script 'extra/setup.py'.
+    ...
+
+    >>> rmdir('extra', 'build')
+
+And update our buildout to use it.
+
+    >>> write('buildout.cfg',
+    ... '''
+    ... [buildout]
+    ... parts = foo
+    ... find-links = %s
+    ...              %s
+    ...
+    ... [foo]
+    ... recipe = recipe
+    ... ''' % (join('recipe', 'dist'), join('extra', 'dist')))
+
+    >>> print system(buildout),
+    Getting distribution for 'recipe'.
+    Got recipe 1.
+    Installing foo.
+
+Now let's change our requirement
+
+    >>> write('buildout.cfg',
+    ... '''
+    ... [buildout]
+    ... parts = foo
+    ... find-links = %s
+    ...              %s
+    ...
+    ... [foo]
+    ... recipe = recipe[extra]:ext
+    ... ''' % (join('recipe', 'dist'), join('extra', 'dist')))
+
+    >>> print system(buildout),
+    Getting distribution for 'extra'.
+    Got extra 1.
+    Uninstalling foo.
+    Installing foo.
+"""
+
 def update_adds_to_uninstall_list():
     """
 
Index: src/zc/buildout/buildout.py
===================================================================
--- src/zc/buildout/buildout.py	(revision 123353)
+++ src/zc/buildout/buildout.py	(working copy)
@@ -1103,9 +1103,15 @@
     __doing__ = 'Loading recipe %r.', spec
     try:
         req = pkg_resources.Requirement.parse(spec)
+        dist = pkg_resources.working_set.find(req)
+        missing_extras = True
+        if dist:
+            missing_extras = None in \
+                             [pkg_resources.working_set.find(r)
+                              for r in dist.requires(req.extras)]
 
         buildout_options = buildout['buildout']
-        if pkg_resources.working_set.find(req) is None:
+        if dist is None or missing_extras:
             __doing__ = 'Installing recipe %s.', spec
             if buildout.offline:
                 dest = None