OBJECTIVE: Wearable activity trackers (WATs) could be a promising strategy to improve physical activity in patients with rheumatic and musculoskeletal diseases (RMDs). The aim was to assess the adherence to and effectiveness of WATs to increase physical activity levels in patients with RMDs. METHODS: A systematic review was performed to identify all cohorts and controlled trials evaluating WATs in patients with RMDs, published between 2000 and 2018, by searching Medline, Embase, PsycINFO, and Cochrane. Data collected pertained to adherence, effectiveness on physical activity, or effectiveness on symptoms (pain, function, quality of life, or fatigue). Meta-analyses were performed with a random effects model. RESULTS: Of 2,806 references, 17 studies were included, with a total of 1,588 patients: 8 studies (47%) in osteoarthritis, 5 (29%) in low-back pain, and 3 (18%) in inflammatory arthritis. Adherence assessed in 4 studies was high (weighted mean +/- SD time worn was 92.7% +/- 4.6%). A significant increase in physical activity was noted (mean difference 1,520 steps [95% confidence interval (95% CI) 580, 2,460], I(2) = 77%; or 16 minutes [95% CI 2, 29] of moderate-to-vigorous physical activity, I(2) = 0%). A significant increase in pain was found for long interventions (>8 weeks) (standardized mean difference 0.25 [95% CI 0.07, 0.43], I(2) = 0%). CONCLUSION: WATs in patients with RMDs had a high short-term adherence, with a significant increase in the number of steps and time spent in moderate-to-vigorous physical activity, although pain should be monitored. WATs may be an effective option to increase physical activity in this at-risk population.