The incidence of congenital anomalies was examined by the level of maternal and paternal smoking during pregnancy for 17,152 infants. A multiple regression analysis was used to control for the possible confounding effects of maternal age, formal education, ethnic origin, religion, marital status, parity, social class, and work outside the home. Neither maternal nor paternal smoking habits were significantly associated with the occurrence of congenital malformations. Maternal age was significantly (P less than .005) related to the incidence of major anomalies. Mothers aged 35 years and older who smoked were found to have a significantly (P less than .002) higher risk for minor malformations and a nonsignificantly increased rate of major malformations. Maternal cigarette smoking may be an important preventable risk factor for congenital anomalies among mothers aged 35 years or older.