Two hundred and sixty-five patients with malignant trophoblastic disease were admitted to the Southeastern Trophoblastic Disease Center at Duke University Medical Center between July 1966 and June 1976. Of these 165 patients, 20 had choriocarcinoma following a term gestation with a survival rate of 60% as compared to 95% survival rate for the remaining 245 patients. Previously described risk factors of initial human chorionic gonadotropin (hCG) titer of greater than 100,000 IU/24 hr urine, duration of symptoms for more than 4 months, significant prior unsuccessful chemotherapy or cerebral or hepatic metastases identified the "poor prognosis" group. Post-term gestation "poor prognosis" patients had a significantly lower cure rate (47%), than other patients with "poor prognosis" for gestational trophoblastic disease (75%; P less than 0.05). Post-term gestation choriocarcinoma has a propensity for more extensive metastatic spread and would appear to be less responsive to conventional chemotherapy, which may be due to an altered immune response in these patients. This suggests that an antecedent term pregnancy should be added to the previously described high-risk factors for patients with malignant trophoblastic disease.