Three sisters in a family with seven children whose grandmother had an ovarian embryonal carcinoma experienced development of malignant and a malignant-like situation in childhood. Two were diagnosed as having malignant germ cell tumors of the ovary, and the third was found to have Langerhans' histiocytosis. The two girls with germ cell tumor shared an identical human leukocyte antigen, whereas the sister with histiocytosis shared one identical haplotype with them. All three children have been treated successfully with chemotherapy and are doing well off of treatment.