Carcinoma in situ (CIS), gonadoblastoma, and early invasive neoplasia were detected in the dysgenetic gonad of a nine-year-old girl with 46,XY gonadal dysgenesis. A close relationship between the three neoplastic components was supported by morphological and immunohistochemical studies. Our findings support the hypothesis that all germ cell tumours, including gonadoblastomas, originate from CIS germ cells formed during early embryonic life.