diff -r 1d811e1097ed Lib/test/test_deque.py
--- a/Lib/test/test_deque.py	Sun Jul 29 19:04:57 2012 +0200
+++ b/Lib/test/test_deque.py	Sun Jul 29 22:06:54 2012 +0300
@@ -7,6 +7,7 @@
 import pickle
 from io import StringIO
 import random
+import struct
 
 BIG = 100000
 
@@ -531,6 +532,21 @@
             gc.collect()
             self.assertTrue(ref() is None, "Cycle was not collected")
 
+    check_sizeof = support.check_sizeof
+
+    @support.cpython_only
+    def test_sizeof(self):
+        BLOCKLEN = 62
+        basesize = support.calcobjsize('2P4nlP')
+        blocksize = struct.calcsize('2P%dP' % BLOCKLEN)
+        self.assertEqual(object.__sizeof__(deque()), basesize)
+        check = self.check_sizeof
+        check(deque(), basesize + blocksize)
+        check(deque('a'), basesize + blocksize)
+        check(deque('a' * (BLOCKLEN // 2)), basesize + blocksize)
+        check(deque('a' * (BLOCKLEN // 2 + 1)), basesize + 2 * blocksize)
+        check(deque('a' * (42 * BLOCKLEN)), basesize + 43 * blocksize)
+
 class TestVariousIteratorArgs(unittest.TestCase):
 
     def test_constructor(self):
diff -r 1d811e1097ed Modules/_collectionsmodule.c
--- a/Modules/_collectionsmodule.c	Sun Jul 29 19:04:57 2012 +0200
+++ b/Modules/_collectionsmodule.c	Sun Jul 29 22:06:54 2012 +0300
@@ -933,6 +933,23 @@
 }
 
 static PyObject *
+deque_sizeof(dequeobject *deque, void *unused)
+{
+    Py_ssize_t res;
+    Py_ssize_t blocks;
+
+    res = sizeof(dequeobject);
+    blocks = (deque->leftindex + deque->len + BLOCKLEN - 1) / BLOCKLEN;
+    assert(deque->leftindex + deque->len - 1 ==
+           (blocks - 1) * BLOCKLEN + deque->rightindex);
+    res += blocks * sizeof(block);
+    return PyLong_FromSsize_t(res);
+}
+
+PyDoc_STRVAR(sizeof_doc,
+"D.__sizeof__() -- size of D in memory, in bytes");
+
+static PyObject *
 deque_get_maxlen(dequeobject *deque)
 {
     if (deque->maxlen == -1)
@@ -995,7 +1012,9 @@
     {"reverse",                 (PyCFunction)deque_reverse,
         METH_NOARGS,             reverse_doc},
     {"rotate",                  (PyCFunction)deque_rotate,
-        METH_VARARGS,           rotate_doc},
+        METH_VARARGS,            rotate_doc},
+    {"__sizeof__",              (PyCFunction)deque_sizeof,
+        METH_NOARGS,             sizeof_doc},
     {NULL,              NULL}   /* sentinel */
 };