A 13-year-old girl had an ovarian Sertoli-Leydig cell tumor associated with marked elevation of the serum alpha-fetoprotein level. On microscopic examination, the tumor had a predominantly retiform pattern and in addition contained heterologous elements in the form of mucinous epithelium, skeletal muscle, and liver cells; alpha-fetoprotein was demonstrated within the liver cells by immunohistochemical techniques. The serum alpha-fetoprotein level fell postoperatively, but rose again when the tumor recurred. Despite radiation therapy and chemotherapy, the tumor pursued a rapidly malignant course and the patient died 9 months postoperatively.