BACKGROUND: Physical exercise has been identified as a potential intervention to improve quality of life in women with breast cancer. We sought to summarize the available evidence concerning the effects of exercise on breast cancer patients and survivors. METHODS: We searched the Cochrane Central Register of Controlled Trials, MEDLINE, EMBASE, CINAHL, PsychINFO, CancerLit, PEDro and SportDiscus as well as conference proceedings, clinical practice guidelines and other unpublished literature resources. We included only randomized controlled trials that examined exercise interventions for breast cancer patients or survivors with quality of life, cardiorespiratory fitness or physical functioning as primary outcomes. We also extracted data on symptoms of fatigue, body composition and adverse effects. RESULTS: Of 136 studies identified, 14 met all the inclusion criteria. Despite significant heterogeneity and relatively small samples, the point estimates in terms of the benefits of exercise for all outcomes were positive even when statistical significance was not achieved. Exercise led to statistically significant improvements in quality of life as assessed by the Functional Assessment of Cancer Therapy-General (weighted mean difference [WMD] 4.58, 95% confidence interval [CI] 0.35 to 8.80) and Functional Assessment of Cancer Therapy-Breast (WMD 6.62, 95% CI 1.21 to 12.03). Exercise also led to significant improvements in physical functioning and peak oxygen consumption and in reducing symptoms of fatigue. INTERPRETATION: Exercise is an effective intervention to improve quality of life, cardiorespiratory fitness, physical functioning and fatigue in breast cancer patients and survivors. Larger trials that have a greater focus on study quality and adverse effects and that examine the long-term benefits of exercise are needed for this patient group.