Objectives: For the purpose of determining the annual incidence and time trends of gestational trophoblastic disease (GTD), the medical records from 24 university hospitals, 13 private general hospitals and the Korean Research Institute of Gestational Trophoblastic Disease (KRI-TRD) were analyzed from 1971 to 1995. Materials & Results: From a total of 7198 GTD cases (H-mole = 3831, Invasive mole = 2163, Choriocarcinoma = 1177, PSTT = 27) among 838659 deliveries between 1971 and 1995, the hospital-based incidence of H-mole per 1000 deliveries declined from 40.2 during 1971-975, to 2.3 during 1991-995. The population-based incidence of H-mole, hwoever, revealed an average of 2.05 per 1000 deliveries during 1991—995. Old age and gravidities as factors in GTD patients both decreased significantly during the study period. Time trends for the incidence of GTD in Korea revealed significant changes, not only a decrease in the incidence of GTD, but also an improvement in the annual remission rate. Korea's socio-eonomic improvement in recent decades also contributed to the decreased incidence of GTD and the increased survival rates.