The indoor and outdoor environmental pollution effects on the respiratory system of 3,559 children aged 9-12 were studied. It was a cross-sectional and interlocal (geographical differentiation) study. The research was conducted during the period between 2000-2001 in five cities of Western Macedonia and more particularly: 1046 children from Ptolemaida, 1249 children from Kozani, 466 from Florina, 419 from Kastoria and 379 from Grevena. The study was performed by means of a questionnaire for the detection of respiratory diseases during childhood, plus spirometry and rhinomanometry measurements. The diachronic quantitative analysis of environmental pollutants was conducted by The Laboratory of Physics of the Atmosphere of the Aristotle University of Thessaloniki. The environmental pollution was found to have a detrimental effect on the respiratory system of children, mainly attributable to the occurrence of rhinitis and infectious bronchitis. The highest prevalence of rhinitis (40.3%) and infectious bronchitis (12.1%) was observed in Ptolemaida, which is a highly polluted region, whereas the lowest (21.2% and 6.7%, respectively) was seen in Grevena, a non-polluted area. As for the indoor pollution, maternal smoking was found to increase the prevalence of respiratory problems in children. Finally, the father's educational level and a past history of nursery school attendance increase the prevalence of respiratory diseases during childhood.