Aims: To define the effects of insulin treatment on body composition and fat distribution, and investigate the potential role of body weight (BWt) gain predictors in patients with poorly controlled type 2 diabetes. , with the FFM increase due solely to total body water [TBW; +2.4 (1.5) l], as there were no detectable changes in total body protein or bone mineral, thereby increasing FFM hydration by 1.3%. More body fat was deposited centrally in patients receiving insulin alone than those receiving insulin with an oral hypoglycaemic agent (metformin). Daily insulin dose, HbA 1 c and hip circumference were independent predictors of BWt gain. Conclusions: Insulin treatment increased fat and FFM similarly in poorly controlled type 2 diabetes patients, with the FFM gain due entirely to TBW. The possible role of metformin in reducing central fat accumulation following insulin treatment warrants further investigation into its mechanism and potential long-term benefits.