Background: Nonalcoholic steatohepatitis (NASH) is common in the morbidly obese. It is a condition that can lead to progressive fibrosis and cirrhosis. We determined the prevalence in a population undergoing bariatric surgery and evaluated the possible serologic predictors before the development of fibrosis. Methods: Liver biopsies were taken from 370 consecutive patients who were undergoing laparoscopic bariatric surgery. The clinical and biochemical parameters were then assessed for correlation with the histologic features of nonalcoholic steatohepatitis. Results: Of the 370 patients, 68 (18%) were found to have NASH. Increased insulin resistance, alanine transaminase, and total bilirubin were independently associated with the presence of NASH. The presence of <2 of the 3 provided the best combination of sensitivity (.71) and specificity (.71) for predicting NASH. Conclusion: Increased insulin resistance, alanine transaminase, and total bilirubin are serologic predictors for the presence of NASH before the development of fibrosis.