Gonadoblastoma is a rare tumor occurring almost exclusively in phenotypic females with intersex disorders and dysgenetic gonads. We report a case of gonadoblastoma in an 18-year old female who was admitted to our hospital for the investigation of primary amenorrhea. The patient underwent bilateral gonadectomy. A histopathologic study revealed streak gonads with extended calcification and bilateral gonadoblastoma. We describe the histopathologic features of gonadoblastoma and the pattern of its potential malignant transformation. Difficulties in the histological diagnosis of this rare tumor are also discussed. The need for early prophylactic removal of dysgenetic gonads, especially in patients that carry the Y chromosome, is emphasized.