<b>Introduction:</b> Few studies have evaluated factors associated with severe asthma in children. Objective: Compare factors associated with severe asthma in children. <b>Methods:</b> Cross-sectional study. We analyzed data from severe and non-severe asthmatic children, aged 2-17 years, in a comprehensive asthma program in Bogotá-Colombia. Qualitative variables were described with absolute and relative frequencies, and quantitative variables with means and standard deviations or medians and interquartile ranges, depending on distribution. Associations were explored with chi-square tests for qualitative variables and Student's t test or Mann-Whitney U test for quantitative variables, depending on distribution. A two-tailed p<0.05 was considered significant. <b>Results:</b> The study had 282 asthmatics, 148 severe and 136 non-severe cases, with a median age of 8. Gender had no association with the severity of asthma. Allergic sensitization was found in 78% of the severe cases, while non-severe asthmatics significantly lacked skin(p=0.001) and serum (p<0.001) sensitization. The history of asthma(p=0.022), rhinitis (p=0.005) and atopy(p=0.023) were significantly more frequent in the severe asthmatics. Viral bronchiolitis occurred in 59% of the severe and 41% of the non-severe cases, being a risk factor in the severe group (p=0.014). In severe asthmatics, chorioamnionitis(p=0.042), respiratory infection in the first year (p=0.030), antibiotic use before 5 years (p=0.028), fast food intake (p<0.001), and vehicular traffic almost all day near the home(p=0.028) were also significant. <b>Conclusion:</b> We found several postnatal factors related to severe asthma in children, the most important being vehicular traffic near the home, fast food intake, bronchiolitis and rhinitis.
