Approximately 8% of all mediastinal tumors are benign teratomas. We reviewed 86 cases of benign teratoma seen at the Mayo Clinic from 1930 through 1981. The mean age of the patients was 28 years and the sex distribution was approximately equal. The most common symptoms were chest, back, or shoulder pain, dyspnea, and cough, but 36% were asymptomatic at the time of presentation. Chest roentgenograms showed a well-circumscribed anterior mediastinal mass which often protruded into one lung field. Detectable calcification was observed in 22 patients: a calcified tumor wall in seven, bone or teeth in the mediastinum of seven, and nonspecific calcifications in eight. Surgical excision remains the best means of diagnosing and treating this benign tumor. Though the tumors are histologically benign, they may present difficult surgical problems because of the vital structures involved. Since 1952 there has been a change in the clinical presentation of patients with this entity: More patients are asymptomatic and have smaller tumors and fewer complications than prior to 1952.