associated with NAFLD, and bariatric surgery (BAS) is traditionally indicated for the treatment of severely obese individuals. Here, we discuss the behavior and prognosis of this liver disease following post-surgical weight loss. Aim: To evaluate the influence of the BAS on the clinical and biochemical parameters of NAFLD in severely obese patients. Methodology: An intervention study included obese individuals (BMI≥ 35kg/m2), who had been submitted to liver biopsy during BAS and had NAFLD. HAIR (hypertension, ALT and insulin resistance and BAAT (BMI, ALT, age and triglycerides) scores and FLI (Fatty Liver Index) were used to compare the patients at the time of surgery, and 12-30 months following weight loss. Results: From October 2004 to September 2007, 122 patients were diagnosed with NAFLD, 40 of whom agreed to participate in the study. The mean age was 37.7 ± 12.5 years, 60% were women and 80% had steatohepatitis (NASH) with fibrosis upon analysis of the liver biopsy performed during BAS. Mean weight loss was 46.0 ± 2.0 kg. After 21 ± 5.8 months of follow-up, a significant improvement was found in all the variables analyzed (79.3% according to the HAIR scores, 95.2% as measured by the BAAT score and 72.5% by the FLI. Conclusion: The results suggest that treatment of obesity by bariatric surgery may influence the prognosis of NAFLD. In addition to weight loss, we observed improvement in the clinical and biochemical parameters related to NAFLD, such as anthropometrics index, hypertension, aminotransferases, triglycerides and insulin resistance.