Cerebral tissue herniation into the middle ear or mastoid are encountered infrequently by the otologist and, therefore, may be misdiagnosed. It might be related to chronic ear infection, previous ear surgery, trauma to the temporal bone, or congenital abnormalities. With advent of antibiotics and improved surgical technique, endaural cerebral hernia has become relatively rare. The authors report a case of cerebral hernia in the mastoid occurring as an insidious complication of chronic otitis media coincidentally discovered at the time of surgery. Pathology and pathogenesis are reviewed and discussed.