OBJECTIVE: The purpose of our study was to identify risk factors for partial molar pregnancy from a woman's general, reproductive, and dietary history. STUDY DESIGN: Sixty-five women with pathologically confirmed partial molar pregnancy were interviewed, and their experiences were compared with those of 130 age-matched control women who had successfully completed a pregnancy with delivery of a live infant at the same hospital during the same calendar period. RESULTS: Multivariate analysis revealed that exposures which independently and significantly predicted increased risk for partial molar pregnancy included irregular cycles, pregnancy histories including only male infants among prior live births, and oral contraceptive use for > 4 years. Dietary factors previously postulated for complete molar pregnancy including protein, fat, vitamin A, or carotene were found not to be related to risk for partial molar pregnancy. CONCLUSION: Epidemiologic patterns for complete and partial molar pregnancies appear to differ somewhat; risk for partial mole is associated with reproductive history but not dietary factors.