A 30-year-old man presented with a history of several convulsive episodes. A CT scan showed a calcified focus in the right temporal lobe. Cerebral angiography yielded no abnormal findings. At craniotomy, the M3 portion of the middle cerebral artery was found to terminate with a blind end at the junction with the calcified mass. A pathological diagnosis of an ossified cerebral aneurysm was made. Calcified cerebral aneurysms are not rare; they are thought to be the result of intra-aneurysmal thrombosis or degenerative changes in the aneurysmal wall. However, complete mural ossification of a cerebral aneurysm is seldom seen, and ossified peripheral middle cerebral artery aneurysms are extremely rare in young individuals. The ossified aneurysm that we report developed over a prolonged period and may have arisen during childhood.