Objective Oral contraceptive use might be associated with cardiometabolic risk in PCOS. We aimed to compare the effects of ethinyl estradioldrospirenone (EE/DRSP) alone vs EE/DRSP plus metformin on clinical and cardiometabolic parameters in PCOS. Design Prospective observational study. Patients Forty-five lean patients with PCOS who received EE/DRSP (30 mu g/3 mg) (n = 25) or EE/DRSP plus metformin (1700 mg/day) (n = 20) and 45 BMI-matched healthy controls. Measurement BMI, waist-to-hip ratio (WHR), hirsutism scores, androgens, lipids, glucose and insulin levels during an OGTT were measured before and after 6 months of treatment in patients and compared to controls. Results At baseline, patients with PCOS showed similar glucose, insulin and lipids but increased 2 h glucose values compared to controls. Hirsutism scores and free androgen index decreased in both treatment groups. BMI and WHR did not show any change in the EE/DRSP group, while metformin addition resulted in a decrease in BMI. Lipid levels increased in both groups. Glucose and insulin parameters did not change in any group, but metformin addition compared to EE/DRSP alone significantly decreased waist circumference, fasting insulin and HOMA-IR. After-treatment values for both EE/DRSP alone and in combination with metformin compared to the control group showed increased 2 h glucose and increased lipids in patients with PCOS. Conclusion EE/DRSP alone or in combination with metformin improves clinical and biochemical hyperandrogenism in lean PCOS. Both treatments similarly alter lipid profile. EE/DRSP alone does not affect insulin sensitivity, whereas combining EE/DRSP with metformin might improve it.