Introduction: Polycystic ovarian syndrome (PCOS) affects 18-22% women of reproductive age. We conducted a systematic review and meta-analysis to quantify expected benefits of lifestyle (exercise and dietary) interventions on various clinical outcomes in PCOS. Methods: Potential studies were identified by conducting systematic search of PubMed, the Cumulative Index to Nursing and Allied Health Literature, and Cochrane controlled trials registry (1966 to April 2013) using key concepts of PCOS, exercise, dietary and lifestyle interventions. Results: Significant improvements were seen in women who received lifestyle intervention vs. usual care, in body composition parameters of body mass index, mean difference (MD) = -0.12 kg.m(-2) (95% CI [-0.22, -0.03], p = .009), body mass MD = -3.42 kg (95% CI [-4.86, -1.99], p < .00001), waist circumference MD = -1.64 cm (95% CI [-2.09, -1.19], p < .00001), waist-hip ratio MD = -0.03 (95% CI [-0.05, -0.01], p = .0002), and body fat % MD = -1.71% (95% CI [-3.10, -0.32], p = .02). Insulin did not improve, MD = -1.21 pmol/L (95% CI [-3.06, -0.63], p = .20). Lipid profile did not improve, total cholesterol MD = -0.02 mmol/L (95% CI [-0.25, 0.21], p = .89). C-reactive protein was significantly lower, MD = -0.47 mmol/L (95% CI [-0.80, -0.15], p = .004). Significant improvements were also observed in cardiorespiratory fitness with exercise alone reducing resting heart rate, MD = -1.89 beats.min(-1) (95% CI [-2.90, -0.88], p = .0002), and peak VO2, MD = 4.86 ml.kg(-1).min(-1) (95% CI [2.83, 6.88], p < .00001). Lifestyle therapy also improved, peak VO2 MD = 5.09 ml.kg(-1).min(-1) (95% CI [3.13, 7.05], p < .00001). Conclusions: Our analyses suggest lifestyle intervention is optimal for improving body composition and cardiorespiratory fitness in women with PCOS.