The objective of this study was to estimate the prevalence of active asthma and identify associated risk factors in adolescents 13 to 14 years of age in Cuiabá, Mato Grosso State, Brazil. A cross-sectional population-based and a subsequently a nested case-control study was conducted in 2008 using the protocol of the International Study of Asthma and Allergies in Childhood (ISAAC). Risk factor analysis used the chi-square test, Fisher's exact test, and binary logistic regression. Variables with p < 0.20 in the bivariate analysis entered the logistic regression model, with six variables remaining in the final model (p < 0.05). Prevalence of active asthma was 19.1%. Risk factors for active asthma (p = 0.01) were: smoking during pregnancy, exclusive breastfeeding < 6 months, family income < 3 minimum wages, female gender, pets currently in the home, and absence of fish in the diet. Prevalence of active asthma was high, but with a significant reduction compared to 1998.