Unlike a number of childhood problems, it is not clear that there are racial or socioeconomic disparities in the prevalence of childhood asthma. We analyzed data from the Child Health Supplement to the 1981 National health Interview Survey, a population-based survey with information concerning 15,416 children, to address the following questions: are there racial or socioeconomic differences in rates of childhood asthma; if yes, what is the contribution of social and environmental characteristics to the observed differences? In this sample, black children were more likely to have asthma than were white children (4.4% vs. 2.5%). Racial disparities in prevalence emerged early and at all childhood ages were due to higher black rates of onset between the ages of 1 and 3 years. Poverty status, maternal cigarette smoking, large family size, smaller size of home, low birth weight, and maternal age younger than 20 years at the child's birth were all associated with increased rates of childhood asthma. When available social and environmental characteristics were controlled for using multivariate analyses, the increased risk for asthma among black and poor children was reduced to statistical insignificance. We conclude that black and poor children in the United States do have higher rates of asthma, that social and environmental factors exert substantial influences on rates of asthma, and that much of the racial and economic disparity in prevalence can be accounted for by a variety of social and environmental characteristics.