Background: Structured physical activity (PA) interventions (ie, intentionally planned) can be implemented in a variety of facilities, and therefore can reach a large proportion of the population. The aim of the authors was to summarize the effectiveness of structured interventions upon PA outcomes, in addition to proportions of individuals adopting and maintaining PA, and adherence and retention rates. Methods: Systematic review with narrative synthesis and exploratory meta-analyses. Twelve studies were included. Results: Effectiveness on PA levels during adoption (pre- to first time point) showed a trivial standardized effect (0.15 [−0.06 to 0.36]); during maintenance (any time point after the first and >6 mo since initiation) the standardized effect was also trivial with a wide interval estimate (0.19 [−0.68 to 1.07]). Few studies reported adoption (k = 3) or maintenance rates (k = 2). Retention at follow-up did not differ between structured PA or controls (75.1% [65.0%–83.0%] vs 75.4% [67.0%–82.3%]), nor did intervention adherence (63.0% [55.6%–69.6%] vs 77.8% [19.4%–98.1%]). Conclusion: Structured PA interventions lack evidence for effectiveness in improving PA levels. Furthermore, though retention is often reported and is similar between interventions and controls, adoption, maintenance, and adherence rates were rarely reported rendering difficulty in interpreting results of effectiveness of structured PA interventions.