A mixed germ cell/sex cord-stromal tumor characterized by the presence of large germ cells which resemble seminoma cells and small cells which resemble Sertoli or granulosa cells. It occurs in the testis and the ovary and is identified in children and adults. It is often associated with gonadal dysgenesis and abnormal karyotype. The disease is gonadoblastoma (MONDO_0010768). Also known as: gonad blastoma.