East Harlem in New York City, a community with a large Puerto Rican population, has among the highest rates of asthma hospitalizations and mortality in the United States, but it is not known if the high rates are related to the ethnic composition, environmental or community factors, or if the higher rates reflect differentials in access to appropriate asthma care. A survey was conducted to: (a) estimate the prevalence of current asthma by ethnicity among school-age children, (b) assess indoor environmental risk factors for childhood asthma, and (c) assess health care utilization and school absences associated with childhood asthma. A cross-sectional survey of parents of elementary school children, using a self-administered questionnaire with a 12-month recall on asthma symptoms based on the International Study of Asthma and Allergies in Childhood. Two public elementary schools in East Harlem (n = 1615 students 5-12 years of age). Among the 1319 respondents (response rate 82%), the prevalence for current asthma (doctor or nurse diagnosis at any time plus wheezing in the past 12 months) was 23%. Puerto Rican children had a prevalence of 35%. Puerto Rican children reported both higher symptomatic frequencies and higher rates of physician diagnosis. Living in a home where cockroaches, rats, or mice had been seen in the past month and with a dust-enhancing heating system also was associated with having asthma, regardless of ethnicity. Compared with other children with asthma, Puerto Rican children with asthma were more likely to live in homes where rats or mice had been seen in the past month. Regardless of ethnicity, children with more frequent, more severe asthma symptoms and incomplete asthma action plans were more likely to have visited the emergency department in the past year. Puerto Rican children were more likely to have missed school because of their asthma in the past year. The prevalence of current asthma was significantly higher among Puerto Ricans, who had higher symptomatic frequency and greater diagnosis rates. Although all children with asthma in the East Harlem study appear to be sensitive to selected indoor environmental risk factors, only Puerto Rican children with asthma appear to be sensitive to the presence of rodents in their buildings. However, their higher school absence rate suggests problems with routine asthma management that could be addressed by improved medical management, programs to help parents manage their children's asthma, or school staff assistance with medications.