The relationship between insulin resistance and serum adiponectin levels in 400 subjects with different obesity-related diseases was studied. Lean subjects with body mass index (BMI) < 25 kg/m(2) were placed in one group and the other five groups of overweight/obese subjects with BMI >or= 25 kg/m(2) were grouped according to disease profile. The homeostasis model assessment insulin resistance (HOMA-IR) index and adiponectin levels were similar in the lean, metabolically normal (MNO) and hypertensive groups, but were different when the dyslipidaemic group was compared with the lean and MNO groups. The type 2 diabetic (DMO) and hypertensive, type 2 diabetic (DMHTO) groups were significantly different from other groups with respect to HOMA-IR index and adiponectin levels. Adiponectin levels were lower in the DMHTO than the DMO group. In multiple regression analysis, adiponectin levels correlated with group categorization independently of age, sex, BMI and HOMA-IR. Hypoadiponectinaemia may play a role in the development of complications of obesity.