GTD occurs in fewer than 1 in 1200 pregnancies in the United States, but it is much more common in Asia and Latin America, where its incidence may be as high as 1 in 200 pregnancies. Risk factors for GTD include advanced or young maternal age, low socioeconomic status, and prior hydatidiform mole. Early diagnosis and prompt treatment are key to a favorable outcome, and thus recognition of the signs and symptoms of the disease is important for all physicians. Because these diseases have low incidences and occur after reproductive events, screening for them in the general population is not worthwhile. No chemopreventive agents have yet been studied in women at risk for GTD, but the oral contraceptive is a good candidate.