The aim of this study was to estimate the prevalence of asthma diagnosis in Brazilian children and to analyze socio-demographic inequalities between the South and Northeast regions of the country. Data for children under 10 years of age were analyzed from the 2003 National Household Sample Survey, or PNAD (n = 69,796). Socioeconomic characteristics, the child's gender and age, and the parent or guardian's skin color were the independent variables investigated through unconditional multiple logistic regression. Prevalence of asthma diagnosis was 8.5% in Brazil as a whole (95%CI: 7.7-8.5) and 12.6% (95%CI: 11.6- 13.5) and 4.4% (95%CI: 4.0-4.8) in the South and Northeast, respectively. After adjustment, children from 3 to 7 years of age and those from the poorest families were more likely to have an asthma diagnosis in both regions. Black skin color, crowding, and substandard housing were associated with asthma in the South. In the Northeast, children of parents with low schooling were less likely to present asthma. The inequalities were more evident in the South, suggesting variation in asthma determinants across the country.