The respiratory system of people who actively and regularly practise sport undergoes systematic changes. The development of the respiratory tract and consequently the tidal volumes depend on the type, intensity, severity, duration and frequency of physical effort. Research indicates that tidal volumes achieved by people who regularly practise sport are higher than in those who have less active lifestyles. The assessment of respiratory system functioning is possible by spirometry, which can help in establishing a correct diagnosis and in monitoring the respiratory system in both healthy people and in patients with chronic diseases. The aim of the study was to evaluate selected parameters of lung function in adolescents who actively practise sport and compare them with the general population. The study involved 180 adolescents, aged 12–17 years. These were 90 boys who actively practised sport in a sports school and 90 boys from a state school who did not train regularly. Sports school students played soccer every day. Spirometry was performed in all the boys who were enrolled in the study. The students who actively played soccer presented significantly higher values of forced expiratory volume in 1 second (FEV1), forced vital capacity (FVC), peak expiratory flow (PEF) and maximal expiratory flow (MEF25). Moreover, a positive correlation was found between the body mass index (BMI) and FEV1, FVC, PEF and MEF25 in the boys who regularly practised sport; in children who did not train regularly, a similar correlation was found only between BMI and FVC. The results indicate that regular training has a positive effect on spirometry parameters in adolescents.