Ultrasound is the modality of choice for evaluating normal or abnormal first trimester pregnancy. Sonography can usually provide a specific diagnosis in abnormal first trimester bleeding. When the sonographic appearance is correlated with the clinical presentation, accurate diagnosis is possible in most cases of gestational trophoblastic disease (GTD). Partial or complete hydatidiform moles can be diagnosed in early gestation. However certain cases will be missed if the curettage material is not sent for pathologic examination. Sometimes molar pregnancies have very unusual sonographic appearances. Sonography and Doppler imaging are helpful in diagnosing gestational trophoblastic disease, in determining whether invasive disease is present, in detecting recurrent disease, and in following the effectiveness of chemotherapy. This pictorial essay describes the pathogenesis, epidemiology, and sonographic spectrum of gestational trophoblastic disease.