Effects of indoor environmental factors on children's respiratory system and pulmonary function tests were investigated in this study. A total of 617 primary school children aged between 9-12 years were included. A standard questionnaire, which includes questions about respiratory symptoms and illness, indoor environmental determinants, family history of respiratory diseases, and smoking habits of the parents, was sent to homes of all children and information was obtained from parents. Children with a family history of asthma, bronchitis, or other chest troubles suffered morning and day/night coughs, shortness of breath, wheezing and asthma, bronchitis, or pneumonia more frequently. Children whose mothers smoked complained of blocked-runny nose and sinusitis more frequently. Pulmonary function levels were diminished in passive smokers and in children whose houses were heated by a wood-burning stove. As a result, passive smoking, using a wood-burning stove for heating, and family history of respiratory diseases are to be considered risk factors for the respiratory system.