Background: Some think that Muslim males and to a lesser extent, even females must be circumcised and this is part of Islam.

The Quran does not mention circumcision at all. What it does say however, implies that it is unnecessary:

God is the Knower of the unseen and the seen, the Mighty the Merciful, Who made most excellent everything that He has created... [32:6-7]

And you see the mountains, you think they are solid, while they are passing by like the clouds. The making of God who made skilfully/perfected everything. He is Expert over what you do. [27:88]

We have created mankind in the best form. [95:4]

It is also implied in The Quran that in certain situations making change to God's creation is wrong (a superstitious practice of the time is cited as an example):

"I will misguide them and make them desire, and I will command them, so that they will mark/cut the ears of the livestock, and I will command them so they will make change to God's creation." Whoever takes the devil as a supporter other than God, then he has indeed lost a great loss. [4:119]

Male circumcision is a traditional practice, also practiced by some Jews/Christians. Female circumcision is a pre-Quran cultural practice native to parts of Africa. The Quran strongly condemns blind following of tradition/culture [2:170, 7:28, 17:36 etc].

Source: http://en.wikipedia.org/wiki/Female_genital_cutting

READ - click to look up verse references