A total of 34 patients with the diagnosis of polycystic ovary syndrome (PCOS) were recruited for this study. Weight distribution in lean PCOS women (n = 17) was 93.5% to 110.5% of normal weight for height and age. In obese women (n = 17) this distribution was 119.5 to 146.5%. Serum testosterone (T), dehydroepiandrosterone sulfate (DHEA-S), delta 4-androstendione (delta 4-A), sex hormone binding globulin, (SHBG), 17-hydroxyprogesterone (17-OH PRG), 17b oestradiol (17b-E2), cortisol (CORT), follicle stimulating hormone (FSH), luteinizing hormone (LH), prolactin (PRL) and insulin (INS) were measured. Serum SHBG levels were lower in obese PCOS women (72.9 +/- 16.2 nmol/l) than in lean PCOS women (99.6 +/- 10.5) (p < 0.001). Fasting insulin levels were higher in obese PCOS women (30.4 +/- 4.5 mUI/ml) than in lean PCOS women (14.2 +/- 7.6 mUI/ml) (p < 0.001). Mean ovarian volume did not differ significantly between lean and obese PCOS women (12.5 +/- 3.7 ml vs 16.1 +/- 5.3, p > 0.5). Endometrial thickness was roughly similar between the two groups. Endometrial surface area in lean PCOS women (7.6 +/- 2.2 cm2) was lower than in obese PCOS women (10.1 +/- 1.9 cm2) and the difference was significant (p < 0.01).