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. © 2014 Springer Science+Business Media New York.244666668Gigante, D.P., De França, G.V., Sardinha, L.M., Temporal variation in the prevalence of weight and obesity excess in adults: Brazil, 2006 to 2009 (2011) Rev Bras Epidemiol, 14 (SUPPL. 1), pp. 157-165. , 22002152 10.1590/S1415-790X2011000500016Kuppan, G., Anjana, R.M., Deepa, M., Inflammatory markers in relation to nonalcoholic fatty liver disease in urban South Indians (2012) Diabetes Technol Ther, 14 (2), pp. 152-187. , 22149546 10.1089/dia.2011.0213Cusi, K., Role of obesity and lipotoxicity in the development of nonalcoholic steatohepatitis: Pathophysiology and clinical implications (2012) Gastroenterology, 142 (4), pp. 711-725. , 22326434 10.1053/j.gastro.2012.02.003Fabbrini, E., Sullivan, S., Klein, S., Obesity and nonalcoholic fatty liver disease: Biochemical, metabolic and clinical implications (2010) Hepatology, 51 (2), pp. 679-689. , 3575093 20041406 10.1002/hep.23280McCullough, A.J., Pathophysiology of nonalcoholic steatohepatitis (2006) J Clin Gastroenterol, 40 (SUPPL. 1), pp. 17-S29. , 16540762Brunt, E.M., Nonalcoholic steatohepatitis (2004) Semin Liver Dis, 24 (1), pp. 3-20. , 15085483 10.1055/s-2004-823098Gastrointestinal surgery for severe obesity: National Institutes of Health Consensus Development Conference statement (1992) Am J Clin Nutr, 55 (2 SUPPL.), pp. 615S-9SMatthews, D.R., Hosker, J.P., Rudenski, A.S., Homeostasis model assessment: Insulin resistance and beta-cell function from fasting plasma glucose and insulin concentrations in man (1985) Diabetologia, 28, pp. 412-419. , 3899825 10.1007/BF00280883Abrams, G.A., Kunde, S.S., Lazenby, A.J., Portal fibrosis and hepatic steatosis in morbidly obese subjects: A spectrum of nonalcoholic fatty liver disease (2004) Hepatology, 40 (2), pp. 475-483. , 15368453 10.1002/hep.20323Guajardo-Salinas, G.E., Hilmy, A., Prevalence of nonalcoholic fatty liver disease (NAFLD) and utility of FIBROspect II to detect liver fibrosis in morbidly obese Hispano-American patients undergoing gastric bypass (2010) Obes Surg, 20 (12), pp. 1647-1653. , 19957049 10.1007/s11695-009-0027-0Boza, C., Riquelme, A., Ibañez, L., Predictors of nonalcoholic steatohepatitis (NASH) in obese patients undergoing gastric bypass (2005) Obes Surg, 15 (8), pp. 1148-1153. , 16197788 10.1381/0960892055002347Kashyap, S.R., Diab, D.L., Baker, A.R., Triglyceride levels and not adipokine concentrations are closely related to severity of nonalcoholic fatty liver disease in an obesity surgery cohort (2009) Obesity (Silver Spring), 17 (9), pp. 1696-1701. , 10.1038/oby.2009.89Shalhub, S., Parsee, A., Gallagher, S.F., The importance of routine liver biopsy in diagnosing nonalcoholic steatohepatitis in bariatric patients (2004) Obes Surg, 14 (1), pp. 54-59. , 14980034 10.1381/096089204772787293Luyckx, F.H., Desaive, C., Thiry, A., Liver abnormalities in severely obese subjects: Effect of drastic weight loss after gastroplasty (1998) Int J Obes Relat Metab Disord, 22 (3), pp. 222-226. , 9539189 10.1038/sj.ijo.0800571De Freitas, A.C., Campos, A.C., Coelho, J.C., The impact of bariatric surgery on nonalcoholic fatty liver disease (2008) Curr Opin Clin Nutr Metab Care, 11 (3), pp. 267-274. , 18403923 10.1097/MCO.0b013e3282fbd33fVargas, V., Allende, H., Lecube, A., Surgically induced weight loss by gastric bypass improves non alcoholic fatty liver disease in morbid obese patients (2012) World J Hepatol, 4 (12), pp. 382-388. , 3554802 23355916Clark, J.M., Alkhuraishi, A.R., Solga, S.F., Roux-en-Y gastric bypass improves liver histology in patients with nonalcoholic fatty liver disease (2005) Obes Res, 13 (7), pp. 1180-1186. , 16076987 10.1038/oby.2005.140Wu, J., You, J., Yerian, L., Prevalence of liver steatosis and fibrosis and the diagnostic accuracy of ultrasound in bariatric surgery patients (2012) Obes Surg, 22 (2), pp. 240-247. , 21901286 10.1007/s11695-011-0509-8Liang, R.J., Wang, H.H., Lee, W.J., Diagnostic value of ultrasonographic examination for nonalcoholic steatohepatitis in morbidly obese patients undergoing laparoscopic bariatric surgery (2007) Obes Surg, 17 (1), pp. 45-56. , 17355768 10.1007/s11695-007-9005-6Grandison, G.A., Angulo, P., Can NASH be diagnosed, graded, and staged noninvasively? (2012) Clin Liver Dis, 16 (3), pp. 567-585. , 3405360 22824481 10.1016/j.cld.2012.05.001