OBJECTIVE: To study the prevalence of acute disease of the lower airways and the role of the domestic environment and maternal smoking. Among the recognized risk factors, passive smoking, living in crowded environments and poor housing conditions play a fundamental role in the causal chain of these diseases. METHODS: A cross-sectional study was carried out in a sample of 775 children aged between 0 and 59 months living in Rio Grande, southern Brazil. Trained interviewers applied a standardized questionnaire to the mothers or guardians of these children in their homes and gathered information about maternal characteristics, housing conditions, socio-economic status of the family and smoking habits. Environmental factors were individually studied, and classified according to a score that evaluated the intensity of their association with respiratory diseases. Bivariate analyses were performed, calculating the prevalence ratios for each risk factor, as well as multivariate ones, by means of non-conditional regression analyses. RESULTS: The main risks identified were: unfavorable environment (P<0.01), less than five years of maternal educational level (P=0.01), monthly family income under US$ 200 (P=0.04), crowded environments (P=0.02), smoking during pregnancy (P=0.03) and present maternal smoking (P=0.01). A thirty-year-old or older mother was identified as offering a protection factor (P=0.05). CONCLUSIONS: These results indicate the need to improve the income distribution, improve the rates of educational level, and combat the smoking habit, particularly concerning mothers. The programs of control of respiratory diseases must address these critical points that represent an important risk to children's health.