Increases in the air pollution levels has well-documented harmful effects on human health, especially exacerbating problems of asthma and other allergies.The prevalence of symptoms associated with asthma was determined in preschool populations in zones with differing levels of air pollution.A cross-sectional study was conducted in Bucaramanga, Colombia, comparing respiratory symptoms in 768 children under seven years in two urban zones with different pollution levels of particulate matter and ozone. Morbidity was evaluated for respiratory indicators of asthma by means of a questionnaire version previously validated in Spanish.The use of cigarettes (27.5%) and aerosols (22.7%) were the most frequent source of indoor air pollution. Wheezing prevalence was 25.6% (95% CI 23.2-29.8%) and diagnosis of asthma was 8.4% (95% CI 6.2-11.5%), with no differences between zones. The final multivariate model did not show an association between outdoor pollution and symptoms related with asthma. However, concrete flooring and presence of mold did show an association with these symptoms.Indoor air quality rather than outdoor air pollution may play a more important role in producing respiratory symptoms related with asthma in preschool children in the city of Bucaramanga, Colombia.