A 21-year-old male with a painful, expanding mass in the occipital bon
e was operated on. The clinical findings were suggestive of a malignan
t tumor. However, appearance and histological examination of the opera
tive specimen identified it as being an aneurysmal bone cyst, a rather
rare nonneoplastic lesion of unknown origin. Besides demonstration of
the case, a review of the relevant literature is presented.