Three infants, 3 months of age or younger with abnormal karyotypes and ambiguous genitalia, had gonadal juvenile granulosa cell tumors. Two of the patients had mixed gonadal dysgenesis and the third had an intersexual disorder of undetermined type. Two tumors arose in undescended testes, and the third in an undescended gonad of uncertain nature. The occurrence of this uncommon neoplasm in these infants indicates that it is another type of neoplasm that may develop in the gonad of a patient with an abnormal karyotype and ambiguous genitalia.