The present analysis aimed to describe the degree of tracking of physical activity over an 8-year follow-up period among a cohort of 557 adolescents in western Norway (13 years of age at baseline). Frequency and time spent in leisure-time physical activity were assessed at ages 13, 14, 15, 16, 18, 19 and 21 years through self-report questionnaires. The cross-sectional results indicated that proportions of adolescents who were physically active declined from 13 to 19 years of age and increased slightly from 19 to 21 years of age. Longitudinally, various measures indicated a weak degree of tracking of physical activity (Pearson's range was .22 for boys and .18 for girls across the 8-year period). The least active persons during early adolescence were those least likely to change during their teenage years. In sum, the findings indicated a weak tendency of tracking of physical activity through adolescence.