Background: The literature is unclear as to whether children and adolescents with chronic respiratory diseases (CRDs) differ from their healthy peers in physical activity (PA). Objective: To determine the PA levels measured through accelerometers in children and adolescents with CRDs. Methods: The authors conducted a systematic review using five databases. The authors included studies that assessed the PA measured by accelerometers in children and adolescents with CRDs. Two independent reviewers analyzed the studies, extracted the data, and assessed the quality of evidence. Results: From 11,497 reports returned by the initial search, 29 articles reporting on 4381 patients were included. In the sensitivity analysis. the authors found that children and adolescents with CRDs had a moderate-to-vigorous PA (MVPA) of -0.08 hours per day (95% confidence interval [CI], -0.12 to -0.03 h/d; P = .001), which was lower than the healthy controls; the values for sedentary time (mean difference -0.47 h/d; 95% CI, -1.29 to 0.36 h/d; P= .27) and steps/d (mean difference 361 steps/d; 95% CI -385 to 1707 steps/d; P= .45) were similar for both. Conclusion: Children and adolescents with CRDs have a slight reduction in MVPA in comparison with healthy controls, but sedentary time and steps/d were similar for both.