Objective: To study the prevalence of respiratory morbidity among passive smoking children and to determine the effects of environmental tobacco smoke in the upper and lower respiratory system of these children in the city of Fortaleza, Ceará, Brazil. Cases and method: This is a cross sectional study of 1,104 children under the 5 years old. Information about respiratory symptoms and illnesses of the children, family history of respiratory diseases, smoking habits of household members and housing conditions were assessed by a questionnaire addressed to the children's parents. Results: Among the 1,104 children, 558 were males and 546 were females. Respiratory morbidity was greater in the children exposed to environmental tobacco smoke than in those who were not exposed (82% vs 74%). Regarding the lower respiratory tract, the most frequent complaints were wheeze (57.7%; OR = 1.32; IC 95%: 1.04-1.68), dyspnea (43.8%; OR = 1.56; IC 95%: 1.22-1.99), asthma, bronchitis or pneumonia (29.4%; OR = 1.31; IC 95%: 1.00-1.71). As to the upper respiratory tract, rhinitis was the most frequent complaint (38.1%; OR = 1.46; IC 95%: 1.13-1.88). Logistic regression analysis showed that the lower respiratory tract complaints were associated with: mother's smoking (OR = 2.02; IC 95% 1.12-3.66); father's smoking (OR = 1.99; IC 95%: 1.16-3.40); mould (OR = 1.55; IC 95%: 1.14-2.13) and family history of respiratory diseases (OR = 1.72; IC 95%: 1.26-2.35). Upper respiratory tract complaints were associated with: family history of respiratory diseases (OR = 1.44; IC 95%: 1.13-1.85) and mother's smoking (OR = 1.54; IC 95%: 1.01-2.35). Conclusion: The authors concluded that the exposure to environmental tobacco smoke is a risk factor for upper and lower respiratory morbidity among children under 5 years old.