Between January 1979 and August 1984, 81 patients with partial molar pregnancy were observed at the New England Trophoblastic Disease Center. The preevacuation clinical diagnosis in 74 (91.3%) patients was either missed or incomplete abortion. The uterine size was either small or appropriate for gestational age in 78 (96.3%) patients. Only five (6.2%) patients presented with excessive uterine size or toxemia and were thought to have a molar pregnancy. Preevacuation human chorionic gonadotropin (hCG) levels exceeded 100,000 mIU/mL in only two (6.6%) of 30 patients. No patient had prominent theca lutein cysts. After evacuation, eight (9.9%) patients developed nonmetastatic gestational trophoblastic disease. Patients with partial moles usually do not present with the clinical features that are characteristic of complete molar pregnancy. The diagnosis of partial mole is generally only considered after histologic review of curettage specimens.