We recently reported that suburban white schoolchildren whose mothers smoked during pregnancy have significantly reduced lung function. Because inner-city and minority children may be at greater risk for respiratory morbidity, we evaluated the relationship between maternal smoking during pregnancy and lung function in 493 white and 383 black schoolchildren 9 to 11 yr of age in three areas of Philadelphia. The child's passive smoking history was determined from reports by the mother. Spirometry was performed at school. After adjusting for height, weight, age, sex, area of city, race, socioeconomic status, and current exposure to environmental tobacco smoke at home, maternal smoking during pregnancy was associated with significant deficits in FEF25-75 (-8.1%) and FEV1/FVC (-2.0%). The observed deficits were larger for black children than for white children, and they were larger for boys than for girls. These results provide additional evidence of an association between maternal smoking during pregnancy and reduced pulmonary function in children, and they suggest that the association may be modified by race and/or sex.