The purpose of this study is to examine variability of hepatic histology as well as expression of key metabolic genes in NAFLD/NASH patients undergoing bariatric surgery. Patients will undergo pre-operative laboratory testing, followed by intra-operative liver and fat biopsies. A 12-month follow up will consist of repeat liver biopsy and laboratory testing. We predict that histologic variability of inflammation and fibrosis in NASH is accompanied by differential gene expression. Furthermore, if this variability is pronounced, this will temper the reliance on percutaneous liver biopsy in NASH as the "gold standard" and further emphasize the need for global markers of disease progression.