We tested the hypothesis that prenatal exposure to cigarette smoke is associated with impaired fertility in adulthood. Fertility for nearly 600 couples was quantified by counting the number of noncontraception cycles required to conceive. Exposure in utero was assessed by asking couples about their parents' cigarette smoking. In contrast to data on laboratory animals, husbands and wives prenatally exposed to cigarette smoke showed no evidence of reduced fertility. In exploratory analyses, prenatal exposure to cigarette smoke was associated with semen abnormalities. Although this observation was based on small numbers, it has biologic plausibility and warrants further investigation.