Background: Reaching an appropriate physical activity level (PAL) in adolescence is an important public health problem. This study aimed to evaluate factors associated with PAL and changes in PAL in late adolescence. Material and Methods: The sample involved 411 adolescents (201 girls) who were 16 years of age at study baseline; the participants completed a structured validated questionnaire at baseline (the beginning of the third grade of high school) and again at follow-up (the end of the fourth grade; when they were 18 years of age). Variables were obtained at both testing waves and included the following predictors: sociodemographic indices (sex, socioeconomic status, parental education), sports factors (participation in individual and team sports, competitive sports achievement, experience in sports), and PAL (the primary outcome), which was measured using the Physical Activity Questionnaire for Adolescents. Results: A significant decrease in PAL between baseline and follow-up testing was evidenced (t-test = 6.17, p < 0.001). A logistic regression model calculated with a dichotomized outcome (normal PAL vs. low PAL), and sex as a covariate, showed a significant influence of participation in team sports and maternal education on PAL, both at baseline (OR = 1.56, 95% CI: 1.11–1.87; OR = 1.38, 95% CI: 1.02–1.90) and at follow-up (OR = 1.45, 95% CI: 1.01–1.90; OR = 1.35, 95% CI: 1.08–1.70, for team sports and maternal education, respectively). Conclusions: The study confirmed certain associations between the studied variables and PAL, but there was no significant influence of the observed indicators on changes in PAL in late adolescence. Further studies evaluating other predictors of changes in PAL are warranted. Med Pr. 2020;71(6):637–47