Nonalcoholic steatohepatitis (NASH) is a form of liver injury that is common in morbidly obese subjects. It has been shown that gender differences exist in the spectrum of nonalcoholic fatty liver disease (NAFLD). The focus of this study was to further characterize these gender differences based on ATP III criteria used to diagnose the metabolic syndrome (MS). We retrospectively assessed NAFLD 58 men and 307 women who underwent gastric bypass, for the presence of NASH, MS, and positive predictors of NASH. There was no statistical difference in age, gender, or the presence of diabetes. The prevalence of NASH in men and women was 60.3% and 30.9%, respectively (P<0.001). Multivariate logistic analysis showed an association of male gender with NASH (2.7; 95% CI, 1.3-5.6, P=0.006) as well as age, AST, and diabetes. MS was diagnosed in 91.4% and 76.2% of men and women (P=0.008), and men tended to have more criteria for MS compared to women. The only positive predictor of MS that was statistically significant between genders was high triglycerides (P=0.003). Controlling for BMI and excess body weight produced similar results. Gender differences do exist within NAFLD and MS, that may be associated with free fatty acid flow to the liver.