A child with unilateral ovarian dysgenesis and marked virilization of external genitalia is reported. Cytogenetic studies revealed sex chromatin in cells from a buccal smear and a karyotype of 46/XX in blood and skin cultures. One gonad was a normal appearing ovary with multiple primordial and mature follicles; the other was a gonadal streak with occasional primordial follicles. During the 10 years in which this patient was observed, growth and development were normal, and chronologically, signs of normal puberty appeared. There was no further virilization since birth. Development of breasts and maturation of vaginal mucosa suggested the beginning of ovarian hormonal activity. A review of the literature failed to reveal a similar case. Current concepts of the timing and mechanisms of disappearance of germ cells from the ovary as well as the etiopathogenesis of virilization in gonadal dysgenesis are discussed.