Cigarette smoking during pregnancy substantially increases the risk of low-weight birth, and infants born to smokers weigh less, on average, than those born to nonsmokers. Low birth weight is an important predictor of neonatal morbidity and death, and the intensity of neonatal care is significantly higher for low-birth-weight infants. In this study, we estimate expenditures on neonatal care based on the relation between maternal smoking during pregnancy and the incidence of low-weight births. Our results indicate that maternal smoking during pregnancy was responsible for 35,816 low-weight births in the U.S. in 1983, or about 14.5% of all low-weight births. We also estimate that 14,977, or 6.6%, of all admissions to neonatal intensive care units were a result of maternal smoking and that these admissions cost approximately $272 million, representing 8.5% of total national expenditures on neonatal intensive care services. We estimate that the average cost of neonatal care was $288 higher for infants born to smokers than for those born to nonsmokers.