Nonalcoholic fatty liver disease (NAFLD) has become an important health issue lately. The aim of this study is to determine its prevalence among obese subjects which undergo Roux-en-Y gastric bypass (RYGB). It is a cross-sectional retrospective study involving 164 subjects who underwent RYGB. Clinical, biochemical, and histopathologic features were evaluated. The most common histopathologic features observed were steatohepatitis with fibrosis (29.9 %) and isolated fibrosis (29.3 %). Increased alkaline phosphatase was associated to NAFLD. Dyslipidemia and type 2 diabetes mellitus were associated to NAFLD. Ultrasound had a global accuracy of 78 % to detect NAFLD. Higher prevalence of severe forms of NAFLD was observed compared to previous reports. Most routine biochemical studies had poor correlation with NAFLD and ultrasound was useful but not definitive to detect NAFLD.