Autogynephilia is a "man’s paraphilic tendency to be sexually aroused by the thought or image of himself as a woman" (Blanchard, 2004). Someone asked if the same phenomenon exists in women. A student from class did some poking around on the CrossDreamers website and found some case studies of autoandrophiliacs, or women who are turned on by thinking of themselves as men. Here is one of the cases:

She enjoyed having sex as a woman with men but also particularly enjoyed living out her sexual fantasy of being male with a penis. She was a self-declared bisexual who, apart from having sex with Robert [her husband] and other couples, would also go off to visit female sex workers herself. She particularly enjoyed the fantasy of raping someone else. This was generally played out with female sex workers who would be accommodating and compliant with the fantasy to her satisfaction. The only male she carried out this sex fantasy with was her husband Robert and at the time of penetrating him she said she clearly envisioned herself as a man with a penis, dominant, powerful and aggressive. Clair was quite clear that although she might run these fantasies in her mind they were just sexual fantasies.

There are several others, all worth reading. You can find them here.