Previous studies examining the relationship between HFE mutations and severity of nonalcoholic steatohepatitis (NASH) have been limited by small sample size or ascertainment bias. The aim of this study was to examine the relationship between HFE mutations and histological severity in a large North American multicenter cohort with NASH. Data from 126 NASH patients were collected from 6 North American centers. Liver biopsy and genotyping for the C282Y and H63D HFE mutations were performed in all subjects. Serum transferrin–iron saturation and ferritin levels as well as hepatic iron content were recorded whenever available. Univariate and multivariate logistic regression analyses were performed to identify factors associated with advanced hepatic fibrosis. The prevalence of heterozygous C282Y and H63D HFE mutations was 14.3% and 21.4%, respectively, in the overall cohort. Among Caucasians, C282Y heterozygotes were more likely to have bridging fibrosis or cirrhosis (44% versus 21% [P = 0.05]) and stainable hepatic iron (50% versus 16% [P = 0.011]) compared with patients with other genotypes. Diabetes mellitus was the only independent predictor of advanced hepatic fibrosis (OR 4.37, 95% CI 1.41-13.54 [P = 0.010]) using multiple logistic regression analysis adjusting for age, sex, ethnicity, body mass index, and HFE genotype status. Conclusion: The HFE C282Y heterozygous mutation is associated with advanced fibrosis among Caucasians with NASH. Additional studies are warranted to examine the possible mechanisms for this relationship. (HEPATOLOGY 2007.)