A review of the classification, biological behavior, clinical diagnosis, and treatment of gestational trophoblastic neoplasms is presented. The events which followed the utilization of chemotherapy as a successful means of therapy are included. Especially important has been the recent recognition that high risk patients, i.e., patients with HCG titers greater than 100,000 IU/24 hr, duration of symptoms greater than four months, and metastasis to the brain and/or liver, with metastatic trophoblastic disease can be managed successfully if treated initially with combination chemotherapy and adjuvant measures including radiation and infusional therapy. Detectable levels of human chorionic gonadotropin are necessary for diagnosis and management of patients with this disease. The lack of sensitivity of commercially available pregnancy tests and the recent ability to determine HCG by means of an antigenically different beta-subunit are discussed.