Although asthma is of frequent occurence, little is known about the factors associated with this disease in Brazil. We studied the association between asthma, environmental and socio-demographic factors in adolescents in Nova lguacu, Rio de Janeiro State. Cross-sectional study using the questionnaires about asthma and environmental factors from the International Study of Asthma and Allergies in Childhood (ISAAC). We performed bivariate analyses between asthma and the factors studied using prevalence ratio (PR), confidence intervals of 95% (95% Cl) and Chi-squared test. Factors associated to asthma in a bivariate analysis were studied using logistic regression and odds ratio (OR). We included 3,033 students, aged 13–14 yrs, selected from 37 schools. The prevalence of asthma was 13.1%. Being female (OR = 1.40; 95%Cl:1.11–1.77), the presence of a mother who smokes (OR = 1.32; 95%Cl:1.04–1.66), a cat in the domicile (OR = 1.32; 95%Cl:1.04–1.69), being the firstborn (OR = 1.34; 95%Cl:1.07–1.68), frequent use of paracetamol (OR = 1.45; 95%Cl: 1.15–1.84), the presence of rhinitis (OR = 5.15; 95%:3.89–6.82) and eczema (OR = 2.35; 95%Cl:1.73–3.19) were independently associated to asthma. Environmental and socio-demographic factors were associated to asthma in adolescents in Rio de Janeiro, irrespective of the presence of others allergic diseases. Interventions acting on these factors may decrease the occurence of asthma in this population.