To evaluate the risk of offspring of heavy drinking during pregnancy, we administered a questionnaire to 633 women at the first prenatal visit. Nutritional status, smoking, drug and alcohol use were determined. Women were classified into three groups: abstinent and rare drinkers; moderate drinkers; and heavy drinkers. After delivery, detailed pediatric, neurologic and developmental examinations were administered by a physician without prior knowledge of any history. Infants born to heavy drinkers had twice the risk of abnormality of those born to abstinent or moderate drinkers (P less than 0.001). Thirty-two per cent of infants born to heavy drinkers demonstrated congenital anomalies, as compared to 9 per cent in the abstinent and 14 per cent in the moderate group (P less than 0.001). Microcephaly and multiple congenital anomalies were much more frequent in this group (P less than 0.001). Heavy drinking during pregnancy increases the risk to offspring.