Objectives: To investigate the therapeutic effects of statins with metformin on polycystic ovary syndrome (PCOS). Settings: Endocrinology department. Participants: MEDLINE, EMBASE and Cochrane Central Register of Controlled Trials were searched until October 2014. Studies comparing statins and placebo, as well as the combination of statins and metformin and metformin alone, were included in the analysis. Interventions: Data were independently extracted by two researchers; any convergence was resolved by a third reviewer. Primary and secondary outcome measures: The following properties were extracted from the qualified trials to identify the effects of statins: clinical variables, metabolic characteristics, hormone outcomes, sign of inflammation, glucose parameters and insulin outcomes. Results: Data from four trials comparing statin and metformin with metformin alone were analysed. The combination of statins and metformin decreases the levels of C reactive protein (standardised mean difference (SMD) −0.91; 95% CI −1.81 to −0.02; p=0.046), triglyceride (SMD −1.37; 95% CI −2.46 to −0.28; p=0.014), total cholesterol (SMD −1.28; 95% CI −1.59 to −0.97; p=0.000) and low-density lipoprotein (LDL) cholesterol (SMD −0.74; 95% CI −1.03 to −0.44; p=0.000). However, the combined therapy fails to reduce fasting insulin (SMD −0.92; 95% CI −2.07 to 0.24; p=0.120), homeostasis model assessment of insulin resistance (SMD −1.15; 95% CI −3.36 to 1.06; p=0.309) and total testosterone (SMD −1.12; 95% CI −2.29 to 0.05; p=0.061). Analysis of the five trials comparing statin with placebo shows that statin monotherapy reduces LDL-cholesterol, triglyceride and total cholesterol. Conclusions: Combined statin and metformin therapy can improve lipid and inflammation parameters, but cannot effectively improve insulin sensitivity and reduce hyperandrogenism in women with PCOS. A large-scale randomised controlled study must be conducted to ascertain the long-term effects of the therapy.