The recognition of adolescents' physical activity has become one of the serious challenges of the modern times, as a concern about the future health of societies. The major goal of the presented study was to discover the level of physical activity among Polish adolescents aged 16-18, and the factors which condition this level. The investigations were carried out in 2011, among 2,974 school adolescents from various locations in Poland - 1,790 girls (60.2%), and 1,184 boys (39.8%). As a study method, a short version of the IPAQ was applied. The results of the study indicated that a larger number of girls than boys show a low level of physical activity. With respect to activity among boys, higher values of intensive and moderate efforts are noted, while in girls, higher values of activities related to walking. It was confirmed that the level of physical activity does not depend on the place of residence. However, the number of physical exercise classes attended is a significant factor, both among boys and girls. It was also found that adolescents who more frequently lead a sedentary style of life are characterized by a lower level of total physical activity. Sedentary lifestyle (time spent sitting) does not differ among the level of physical activity of girls and of boys, neither with respect to the scope of the total physical activity nor to its three levels (low, moderate, high).