To determine the incidence of choriocarcinoma in the United States, the authors examined data from the Surveillance, Epidemiology, and End Results (SEER) Program, 1973–1982, the National Center for Health Statistics, and the Centers for Disease Control. They calculated an overall incidence of one per 24,096 pregnancies or one per 19,920 livebirths. Among whites, who comprised the majority of cases, the incidence was estimated to be one per 22,623 livebirths. After adjustment for age and birth effects, whites demonstrated the lowest rates, with blacks and other races at 2.1- and 1.8-fold elevated risk, respectively. The incidence among whites increased dramatically with maternal age, with women aged 40–44 years at an 8.6-fold excess risk compared with those aged 20–24 years. In addition, teenagers who gave birth were at higher nsk. Possible reasons for these incidence patterns are discussed.