An analysis of 233 patients with complete hydatidiform mole admitted to Hacettepe University Hospital between 1964 and 1988 has been carried out. Methotrexate was administered prophylactically to 19 of 120 low-risk and to 52 of 113 high-risk patients. The difference in the incidence of postmolar gestational trophoblastic disease between prophylactically untreated and treated groups of either low-risk (13.9% versus 5.3%, P greater than 0.01) or high-risk (26.2% versus 25.0%, P greater than 0.01) patients was found to be statistically insignificant. Drug toxicity and mortality rates were 16.9% and 2.8%, respectively. It is concluded that prophylactic chemotherapy is not highly effective in the prophylaxis of postmolar gestational trophoblastic disease. Strict follow-up through sensitive betahuman chorionic gonadotropin assays should be the standard management of postmolar patients.