Of 74 Jewish patients with histologically confirmed hydatidiform mole (HM), 37 (50%) were referred to the hospital after the 15th week of pregnancy. In only 5.4% was HM the referral diagnosis. A correct diagnosis prior to uterine evacuation was made in only 29 (39.2%), and this was mainly when the uterus was normal or larger than expected for gestational age. The percentage with urinary human chorionic gonadotropin hemagglutination inhibition titers below 100,000 U/liter was significantly smaller in those with a smaller uterus as compared with those with a uterus of normal size or larger than expected. The incidence of persistent trophoblastic disease (PTD) following HM without the use of prophylactic chemotherapy was 12.2%. Patients with a large-for-date uterus had a greater potential for this outcome. All patients with PTD responded well to treatment, which consisted mainly of chemotherapy, and remained free of disease after therapy was completed.