Serum lipocalin-2 levels are elevated in obese patients. We assessed serum lipocalin-2 levels in polycystic ovary syndrome (PCOS) and the effects of weight loss or metformin on these levels. Forty-seven overweight/obese patients with PCOS [body mass index (BMI) >27 kg/m(2)] were instructed to follow a low-calorie diet, to exercise and were given orlistat or sibutramine for 6 months. Twenty-five normal weight patients with PCOS (BMI <25 kg/m(2)) were treated with metformin for 6 months. Twenty-five normal weight and 25 overweight/obese healthy female volunteers comprised the control groups. Serum lipocalin-2 levels did not differ between overweight/obese patients with PCOS and overweight/obese controls (p = 0.258), or between normal weight patients with PCOS and normal weight controls (p = 0.878). Lipocalin-2 levels were higher in overweight/obese patients with PCOS than in normal weight patients with PCOS (p < 0.001). In overweight/obese patients with PCOS, weight loss resulted in a fall in lipocalin-2 levels (p < 0.001). In normal weight patients with PCOS, treatment with metformin did not affect lipocalin-2 levels (p = 0.484). In conclusion, PCOS per se is not associated with elevated lipocalin-2 levels. Weight loss induces a significant reduction in lipocalin-2 levels in overweight/obese patients with PCOS.