OBJECTIVE: To analyze the trends in asthma prevalence in children and adolescents between 1998 and 2008 in Brazil. METHODS: Data on asthma prevalence from the 1998, 2003 and 2008 National Household Sample Surveys were analyzed. The sample was comprised of 141,402, 144,443 and 134,032 individuals in 1998, 2003 and 2008, respectively, and the analysis was adjusted for the sample design. Trends in asthma prevalence were described for sex, Brazilian regions and place of residence of children (zero to nine years of age) and adolescents (ten to 19 years of age). RESULTS: The prevalence of asthma in children was 7.7% in 1998, 8.1% in 2003 and 8.5% in 2008, with an annual increase of 1%. The highest annual increase was observed in the Southeast and North regions (1.4%). Among adolescents, the prevalence of asthma was 4.4% in 1998, 5.0% in 2003 and 5.5% in 2008, with an increase of 2.2% per year. In the Northeast region, the annual increase in the prevalence of asthma was 3.5%. The greatest increases were observed in boys and in residents of rural areas. CONCLUSIONS: Although asthma has decreased in some developing countries, the results found in Brazil point to an increase in this disease in children and adolescents between 1998 and 2008, especially in rural areas.