Aims: The purpose was to describe the patterns of commuting to school in young people and to examine its associations with physical activity (PA) and cardiorespiratory fitness. Methods: The sample comprised 2271 Estonian and Swedish children and adolescents (1218 females) aged 9-10 years and 15-16 years. Data were collected in 1998/99. Mode of commuting to and from school was assessed by questionnaire. Time spent (min/day) in PA and average PA (counts/min) was measured by accelerometry. Cardiorespiratory fitness was assessed by means of a maximal cycle ergometer test. Results: Sixty-one percent of the participants reported active commuting to school (ACS). Estonian youth showed lower levels of ACS than Swedish (odds ratio, 0.64; 95% confidence interval, 0.53-0.76) and girls reported lower levels than boys (0.74; 0.62-0.88). ACS boys showed higher PA levels than non-ACS boys for moderate, vigorous, MVPA, and average PA levels (all p <= 0.01). Participants who cycled to school had higher cardiorespiratory fitness than walkers or passive travellers (p < 0.001). Conclusions: Nearly two-thirds of the participants actively commuted to school. ACS may provide an opportunity to increase levels of daily PA, especially in boys, and cardiorespiratory fitness, especially if cycling. Public health strategies should develop and test ACS patterns to get more evidence and promote bike-friendly environments.