Nonseminomatous germ cell tumor with very high serum human chorionic gonadotropin. Most patients with disseminated nonseminomatous germ cell tumor (NSGCT) have an excellent prognosis with modern chemotherapy, although certain subgroups with a worse prognosis have been described. One such subgroup includes patients with high serum levels of the tumor marker, human chorionic gonadotropin (HCG). Sixteen patients of 104 treated for NSGCT at the CRC Wessex Medical Oncology Unit (Southampton, UK) presented with serum HCG greater than 25,000. Most of these patients exhibited features of the "choriocarcinoma syndrome" with bulky, rapidly progressive disease; frequent pulmonary, hepatic, and central nervous system complications; and a generally poorer response to standard NSGCT chemotherapy. Histologic identification of trophoblastic tumor was not made in all patients and is not essential for the diagnosis of the syndrome; indeed, closed biopsy may be contradicted in some circumstances because of the risk of hemorrhage. The NSGCT patients with poor prognosis, including patients with the choriocarcinoma syndrome, must be clearly identified in order to improve management and, eventually, cure rates. 