The aim of this study was to estimate the prevalence of asthma and associated factors among students 13 and 14 years of age in São Luís, Maranhão State, Brazil. A cross-sectional study was conducted using the questionnaire developed by ISAAC (International Study of Asthma and Allergies in Childhood) and an additional questionnaire from July 2008 to May 2009, including 3,069 adolescents. Asthma prevalence (wheezing in the previous 12 months) was 12.7%, lifetime prevalence was 32.4%, 3.9% reported difficulty speaking due to wheezing, and 9.8% reported wheezing after exercise. In the multivariate analysis, factors associated with increased asthma prevalence were family history of asthma, respiratory infection and wheezing in early life, eczema, allergic rhinitis, and passive smoking. Asthma prevalence was lower than for Brazil as a whole. Factors most strongly associated with asthma prevalence in these adolescents were family history of asthma (PR = 3.86), wheezing in early childhood (PR = 4.58), and allergic rhinitis (PR = 3.21).