The clinical and pathological features of 207 ovarian Sertoli-Leydig cell tumors from our consultation and hospital files were reviewed. The patients ranged in age from 2 to 75 (average 25) years. Seventy-five percent of them were 30 years of age or younger and less than 10% were over 50 years of age. One-third of the patients presented because of unequivocal evidence of androgen excess, and an additional 10% had a history suggesting androgen excess; most of the remaining patients complained of abdominal swelling or pain. At operation, 97.5% of the tumors were Stage I, 1.5% were Stage II, and 1% were Stage III. Both ovaries were involved in 1.5% of the cases. The tumors ranged from microscopic to 51 cm in diameter (average 13.5 cm); 15% of them were ruptured. Thirty-eight percent of the tumors were solid, 58% were solid and cystic, and 4% were cystic. The solid tissue was typically lobulated and yellow. On microscopic examination, 11% of the tumors were well differentiated, 54% were of intermediate differentiation, 13% were poorly differentiated, and 22% contained heterologous elements according to the criteria of the World Health Organization; a prominent retiform pattern was present in 15% of them. Follow-up was obtained for 164 patients. The tumor was clinically malignant in 18% of them. The prognosis correlated most meaningfully with the stage and degree of differentiation of the tumor. The high-stage tumors were all clinically malignant. All the well-differentiated tumors were benign, but 11% of those of intermediate differentiation, 59% of the poorly differentiated tumors, and 19% of those with heterologous elements were malignant. In a few cases radiation therapy, chemotherapy, or a combination of the two, in addition to surgical excision, was of benefit in the management of the malignant tumors.