A systematic review and meta-analysis of randomized controlled trials to determine if motivational interviewing leads to increased physical activity, cardiorespiratory fitness or functional exercise capacity in people with chronic health conditions.Seven electronic databases (MEDLINE, PsychINFO, EMBASE, AMED, CINHAL, SPORTDiscus and the Cochrane Central Register of Controlled trials) were searched from inception until January 2014.Two reviewers independently examined publications for inclusion. Trials were included if participants were adults (>18 years), had a chronic health condition, used motivational interviewing as the intervention and examined physical activity, cardiorespiratory fitness or functional exercise capacity.Two reviewers independently extracted data. Risk of bias within trials was assessed using the Physiotherapy Evidence Database Scale.Meta-analyses were conducted with standardized mean differences and 95% confidence intervals (CIs) were calculated. The Grades of Recommendation, Assessment, Development and Evaluation approach was used to evaluate the quality of the evidence.Eleven publications (of ten trials) were included. There was moderate level evidence that motivational interviewing had a small effect in increasing physical activity levels in people with chronic health conditions relative to comparison groups (standardized mean differences = 0.19, 95% CI 0.06 to 0.32, p = 0.004). Sensitivity analysis based on trials that confirmed treatment fidelity produced a larger effect. No conclusive evidence was observed for cardiorespiratory fitness or functional exercise capacity.The addition of motivational interviewing to usual care may lead to modest improvements in physical activity for people with chronic health conditions.