Background: Animal studies demonstrated that early exposure to phenobarbital decreases reproductive function. This study investigates whether prenatal exposure to these anticonvulsants affects human genital tract development. Methods: Genital anomalies at birth were studied retrospectively in 90 phenobarbital-exposed, 108 phenobarbital plus phenytoin-exposed, and 198 matched control infants. Of this group, 72 drug-exposed males, 75 drug-exposed females, and 147 matched control subjects participated in a follow-up and were interviewed at age 19-35. Differences between groups were tested by chi-square and t-tests. Results: A total of 15% of the phenobarbital-exposed boys versus 2.8% control boys had undescended testes at birth. More anticonvulsant-exposed (24%) than control males (11%) had received medical treatment for genital anomalies. Anticonvulsant-exposed females more often had irregularities in menstrual cycles (31% vs 17%) and bleeding (15% vs 3%) and reported more problems during pregnancy. Conclusions: Prenatal exposure to anticonvulsants seems to induce minor genital anomalies and may affect reproductive function.