BACKGROUND: Despite the clinical recommendation of exercise and diet for people with knee osteoarthritis (OA), there are no systematic reviews synthesising the effectiveness of combining physical activity and dietary restriction interventions on the musculoskeletal function of overweight and obese older adults with knee OA. OBJECTIVE: To evaluate the effectiveness of combined physical activity and dietary restriction programmes on body weight, body mass index (BMI) and the musculoskeletal function of overweight and obese older adults with knee OA. INFORMATION SOURCES: A detailed search strategy was applied to key electronic databases (Ovid, Embase, Web of Science andCumulative Index to Nursing and Allied Health Literature (CINAHL)) for randomised controlled trials (RCTs) published in English prior to 15 January 2017. PARTICIPANTS: Participants with BMI ≥25 kg/m(2), aged ≥55 years of age and with radiographic evidence of knee OA. INTERVENTIONS: Physical activity plus dietary restriction programmes with usual care or exercise as the comparators. OUTCOME MEASURES: Primary outcome measures were body weight, BMI or musculoskeletal function. Secondary outcome measures were pain and quality of life. RESULTS: One pilot and two definitive trials with n=794 participants were included. Two articles reporting additional data and outcome measures for one of the RCTs were identified. All included RCTs had an unclear risk of bias. Meta-analysis was only possible to evaluate mobility (6 min walk test) at 6 months and the pooled random effect 15.05 (95% CI -11.77 to 41.87) across two trials with n=155 participants did not support the combined intervention programme. Narrative synthesis showed clear differences in favour of a reduced body weight and an increased 6 min walk in the intervention group compared with control groups. CONCLUSION: The quality of evidence of benefit of combining exercise and dietary interventions in older overweight/obese adults with knee OA is unclear. TRAIL REGISTRATION NUMBER: CRD42015019088 and ISRCTN, ISRCTN12906938.