Adolescence may be a period particularly relevant for acquisition of lifelong habits of physical activity (PA). We investigated the tracking of leisure-time PA from 13 to 17 years old and the influence of urban environment and other determinants. As part of the EPITeen cohort (Portugal), we evaluated 969 adolescents living in the city of Porto. Participants were assembled in public and private schools at 13 years and reevaluated at 17 years. Leisure-time PA was evaluated by self-reported questionnaires. The shortest routes from residence to urban green spaces and open sports spaces were calculated using the street network within a Geographical Information System. Odds ratio (OR) and 95% confidence intervals were calculated by multinomial logistic regression. Among sedentary girls at 13 years, 33.1% were still sedentary at 17 years, 39.8% changed to low, 22.3% to moderate, and only 4.6% changed to vigorous PA. In boys, the respective values were 32.3%, 17.3%, 36.2%, and 14.2%. High PA levels were maintained by 19.5% of the girls and by 41.1% of the boys. After adjustment for parental education and body image at 13 years, practice of sports at 13 years was strongly associated with stable high PA at 17 years: in girls OR ¼ 3.96 (2.21, 7.12); in boys OR ¼ 6.81 (3.30, 14.07). Distance to urban green spaces or to open sports spaces was not associated to changes in leisure-time PA. Practice of sports in early adolescence may be important to promote maintenance of high PA. Urban environment in the vicinity of residence did not affect changes in the practice of leisure-time PA.