Previous studies have reported increasing trends in physical activity in the Finnish population. These reports have not, however, included the perspective of cardiorespiratory stress in adolescent and young adults. We examined the present patterns of physical activity among Finnish adolescents and young adults in 1992. We specifically assessed whether the young people experience the volume of physical activity that is believed to stress the cardiorespiratory system appropriately in order to increase the level of fitness. The subjects in the present study were participants of a large multicenter study of atherosclerosis precursors in children and young adults. Physical activity was measured with a self-administered questionnaire in 2255 adolescents and young adults (1015 males and 1240 females). The proportion of subjects undertaking the volume of physical activity believed to benefit the cardiorespiratory system appropriately was 19%. The proportion was higher in males than in females (26 vs 13%). The proportion of active subjects became smaller in older age groups in both sexes. Half the study population (51% of the males; 48% of the females) reported frequent leisure-time physical activity less than once a month. In conclusion, Finnish adolescents and young adults have low levels of physical activity on the average, and many young Finns seldom undertake the volume of physical activity believed to benefit the cardiopulmonary system. Young males seem to be physically more active than females.