Pelvic ultrasonography was performed in 33 patients with persistent gestational trophoblastic disease (GTD) and the sonographic findings were compared in all patients with laparoscopic findings and histologic material from endometrial curettage and/or hysterectomy. Ultrasonography indicated trophoblastic uterine involvement in 17 patients (51.5%) and the ultrasound interpretation was histologically confirmed in all 17 patients by endometrial curettage and/or hysterectomy. Among the 16 patients in whom the uterus appeared normal by ultrasound, endometrial curettings demonstrated scanty fragments of trophoblastic tumor in 6 patients (37.5%). Furthermore, in all 16 patients in whom the uterus appeared normal by ultrasound, laparoscopy also revealed no uterine abnormalities. Ultrasonography appears to be accurate in detecting extensive trophoblastic uterine involvement and helpful in identifying resistant uterine foci. Pelvic ultrasonography should be an integral part of the pretreatment assessment of patients with persistent GTD.