Objective: To meta-analyze the prevalence and predictors of dropout rates among adults with fibromyalgia participating in exercise randomized controlled trials (RCTs). Data Sources: Two authors searched Embase, CINAHL, PsycARTICLES, and Medline up to 01/21/2023. Study Selection: We included RCTs of exercise interventions in people with fibromyalgia that reported dropout rates. Data Extraction: Dropout rates from exercise and control conditions and exerciser/participant, provider, and design/implementation related predictors. Data Synthesis: A random effects meta-analysis and meta-regression were conducted. In total, 89 RCTs involving 122 exercise arms in 3.702 people with fibromyalgia were included. The trim-and-fill-adjusted prevalence of dropout across all RCTs was 19.2% (95% CI=16.9%-21.8%), which is comparable with the dropout observed in control conditions with the trim-and-fill-adjusted odds ratio being 0.31 (95% CI=0.92-1.86, P=.44). Body mass index (R2=0.16, P=.03) and higher effect of illness (R2=0.20, P=.02) predicted higher dropout. The lowest dropout was observed in exergaming, compared with other exercise types (P=.014), and in lower-intensity exercises, compared with high intensity exercise (P=.03). No differences in dropout were observed for the frequency or duration of the exercise intervention. Continuous supervision by an exercise expert (eg, physiotherapist) resulted in the lowest dropout rates (P<.001). Conclusions: Exercise dropout in RCTs is comparable with control conditions, suggesting that exercise is a feasible and accepted treatment modality; however, interventions are ideally supervised by an expert (eg, physiotherapist) to minimize the risk of dropout. Experts should consider a high BMI and the effect of the illness as risk factors for dropout. © 2023 American Congress of Rehabilitation Medicine