Preoperative clinical and biochemical data and intraoperative liver biopsy of 1,000 obese patients submitted to biliopancreatic diversion (BPD) were analyzed, and correlations investigated. Of 2,645 patients submitted to BPD between May 1976 and November 2002, the last 1,000 consecutive obese patients with no history of alcohol consumption or infectious hepatitis were selected. Clinical data included: age, body weight, BMI, waist-to-hip ratio (W/H), arterial blood pressure, serum glucose, triglycerides, cholesterol, albumin/γ-globulin ratio, total, conjugated and unconjugated bilirubin, γ-GT, alkaline phosphatase, AST, ALT, and prothrombin time. The degree of steatosis, inflammation and fibrosis on intraoperative wedge liver biopsy was determined and scored. Liver steatosis >70% and presence of bridging fibrosis were analyzed separately. Mean BMI was 48 kg/m². 263 patients had steatosis of >70%, and 79 had bridging fibrosis. Regression analysis showed an association between steatosis and AST, ALT, AST/ALT ratio, body weight, W/H, serum glucose, serum tryglicerides, BMI, γ-GT, age, and unconjugated bilirubin. Inflammation was significantly greater in older patients. Patients with bridging fibrosis had significantly higher values of serum glucose, AST, γ-GT, serum cholesterol and were significantly older. Bridging fibrosis was associated with diabetes, W/H >1, hypertension, albumin/γ-globulin ratio <1. Severe steatosis and bridging fibrosis seem to be associated with the metabolic syndrome. No reliable biochemical data could identify patients with severe chronic liver damage with sufficient sensitivity to avoid liver biopsy for diagnosis and staging of the disease.