Two children had prepubertal XY gonadal dysgenesis. A 7-year-old girl with clitoral enlargement had a left ovarian tumor that contained a dysgerminoma; the right gonad proved to be a gonadoblastoma. The second child (a 2-year-old girl) showed poor physical development and slight virilization of the genitalia. Her bilateral dysgenetic gonads were removed at exploratory laparotomy. The occurrence of gonadal tumors in XY gonadal dysgenesis is increased. It is probably related to the hypergonadotropinism existing from childhood as well as to genetic predisposition of the cryptorchid testis in the presence of a Y chromosome. Our first patient is one of the youngest who had XY gonadal dysgenesis iwth gonadoblastoma reported. The indication of prophylactic gonadectomy in XY gonadal dysgenesis is emphasized.