Gonadoblastoma occurs almost entirely in patients with pure mixed gonadal dysgenesis or in male pseudohermaphrodites. A report of a patient with monolateral gonadoblastoma who sought consultation for primary amenorrhea is presented. Telarche and adrenarche occurred spontaneously at age 12. No signs of clitoromegaly or hirsutism were present. Endoscopic examination and biopsy specimens revealed absence of uterus, monolateral gonadoblastoma and controlateral teratoma in normally developed gonads. Serum gonadotrophins, estrogens and progesterone levels showed a biphasic secretion pattern. 46, XX karyotype was found on peripheral blood cells, skin fibroblasts and ovarian tissue.