Obesity represents one of serious risk factors in chronic renal failure patients (CRF). In three years prospective double-blind randomised multicentre study we monitored 66 patients with advanced chronic renal insufficiency, GFR 24.4-37.3 ml/min (0.41 to 0.62 ml/s) and BMI > or = 30 kg/m2 on long term low-protein diet (0.6 P/kg BW/day) and ACEI + ARB. Thirty four randomly selected patients (group I) were treated with keto amino acids, 32 patients in control group (group II) with placebo. During the study period significant decrease of BMI, proteinuria and slowing in progression of renal failure (C(in)) were found. Significant changes were also noted in parameters of albumin and transferrin (p < 0.02), leucin and WQ (p < 0.01 - p < 0.02), glycaemia and HbA1c (p < 0.02), triglycerides (p < 0.01), leptin and ObRe (p < 0.01) and selected parameters of endothelial dysfunction (ET1, p < 0.02, TGFbeta1, p < 0.02). Significantly also decreased PTH value (p < 0.01). Successful treatment of obesity can significantly improve long term prognosis in CRF patients.