Osteomas are benign, slow growing tumors of bone that occur almost exclusively in the craniofacial region. They are uncommon in the temporal bone. Surgical excision is indicated in symptomatic cases. An osteoma arising from the lateral semicircular canal growing into the mastoid cavity is extremely rare and usually discovered on routine radiography. We present a case of osteoma arising from the lateral semicircular canal growing into the mastoid cavity, followed by a discussion of the etiology, presentation, and management of osteomas.