The number of children admitted to hospitals because of asthma has been reported to decrease in Sweden in recent decades despite an increasing prevalence of childhood asthma. This decrease has been explained by improved maintenance therapy of children with severe asthma. In this study we used data on hospital admissions for asthma from the Swedish National Patient Discharge Registers in Stockholm, Malmö and Gothenburg 1990-1994 to identify social and ethnic characteristics of children 2-18-y-old in need of improvement in disease management. Children in families on social welfare (adjusted odds ratios (OR): 1.3 and 1.5) and children in single-parent households (adjusted OR: 1.3 and 1.4) were more often admitted to hospital because of asthma at least once during a calendar year in the 2-6- and 7-18-y-old groups. Children in families on social welfare had a particularly high risk of being admitted more than once during a calendar year (adjusted OR: 1.6 in the younger age group and 2.9 in the older group). Exposure to smoking during pregnancy was more common in socially disadvantaged families and increased the risk of hospital admission in children below 3 y of age. Children born outside Western Europe, the USA and Australia were less commonly admitted to hospital because of asthma than other children in the population (adjusted OR: 0.1-0.5). Swedish-born children with mothers who were born in Eastern and Southern Europe were also at lower risk for admission to hospital with a diagnosis of asthma (adjusted OR: 0.2-0.6). This probably indicates a lower prevalence of asthma in these ethnic groups. Further studies are needed to identify factors that can explain these ethnic differences in childhood asthma.