Non-alcoholic steatohepatitis (NASH) is a frequent accompaniment of morbid obesity. On occasion NASH can lead to progressive fibrosis, cirrhosis, and liver failure. Bariatric surgery producing profound weight loss has been shown to alter the course of this disease. Early recognition of NASH may identify patients at risk and modify follow-up. We sought to determine what preoperative indicators might point to NASH and justify intraoperative liver biopsies at the time of bariatric surgery. Patients without known liver disease to undergo bariatric surgery were prospectively evaluated preoperatively (age, gender, race, BMI, diabetes mellitus, hypertension) including a panel of liver function tests (AST, ALT, GGTP, prealbumin) and lipid levels (cholesterol, triglycerides). Routine core liver biopsies were then obtained at the time of Roux-en-Y gastric bypass. Biopsies were obtained on 141 evaluable patients (BMI 54 +/- 10, age 44 +/- 11). There were 29 males and 46 diabetics. Features of NASH or NASH associated fibrosis were found in 57 patients (40%). By univariate analysis male gender (OR 2.53, p = 0.04), diabetes mellitus (OR 2.68, p = 0.007), triglycerides (OR 1.003, p = 0.01), prealbumin (OR 0.94, p = 0.04), and GGTP (OR 1.013, p = 0.01) were significantly associated with NASH. Elevated AST (p = 0.051), ALT levels, and AST/ALT ratios were not. By logistic regression only triglycerides (OR 1.004, p = 0.02) and prealbumin (OR 0.89, p = 0.005) were independent predictors of NASH when considered as continuous variables. The results of this study show that clinical factors - age, gender, diabetes mellitus, and BMI - as well as routine liver function tests, including transaminase levels, do not identify patients at risk for NASH. Triglycerides may serve as a priming event for NASH while low prealbumin may signify early impairment of protein synthesis in NASH reflecting subtle hepatocellular dysfunction. In our study, traditional liver transaminases did not help to select patients with steato-inflammation. Elevated AST levels approached but did not quite attain statistical significance. However, elevated triglycerides and depressed prealbumin were linked with NASH or NASH associated fibrosis and could be used clinically to identify surgical bariatric patients in whom an intraoperative liver biopsy should be performed.