Is that a phantom in your pocket, or are you happy to see me?

Phantom limb syndrome is a well documented and apparantly quite common phenomenon among amputees. It's the sensation that a missing limb is still there, and even responding to stimuli. But the upper and lower extremities (i.e. legs and arms) aren't the only body parts surgically removed. What happens, for example, when a man has his penis removed as part of a sex-change operation? Wonder no more:

[R]eports on the phantom penis and its treatment are very rare. We experienced a patient who underwent sex reassignment surgery in whom the sensation of a phantom erectile penis persisted.

The case study, publised in Acta Medica Okayama this past year, is freely available here (and complete with pictures) and describes the case of a 52-year old man who had male-to-female transgender surgery. Phantom erections are quite common after penis amputation either from sex reassignment or trauma (such as being assaulted by Lorena Bobbitt) but usually stop after a couple of weeks. This man's persisted for over 6 months before he returned to the operating room to have it fixed. The surgeons removed some of the underlying erectile tissue shortly after which the invisible hard-on disappeared. Neurotopia has a more detailed discussion of this case, and the underlying neurology of phantom limbs in general.