BACKGROUND: Morbid obesity is strongly associated with non-alcoholic fatty liver disease. The effects of bariatric surgery on liver tests an histological abnormalities after weight loss are controversial. AIM: To review the literature on the prevalence of non-alcoholic fatty liver disease in patients with morbid obesity with respect to laboratory and histopathological parameters and the effect of weight loss on these parameters after bariatric surgery. RESULTS: Standard liver tests do not seem to be a sensitive tool for the assessment and follow-up of non-alcoholic fatty liver disease in obesity. In nearly all patients with morbid obesity, histological abnormalities reflecting non-alcoholic fatty liver disease are present. Bariatric surgery in these patients will decrease the grade of steatosis. However, there are some concerns about the effect of bariatric surgery on hepatic inflammation and fibrosis. In particular, older follow-up studies reported negative results as opposed to more recent studies, which also showed improvement in hepatic inflammation and fibrosis. Unfortunately, most studies had limitations because of the selection of patients. CONCLUSION: Despite limitations in many studies, bariatric surgery seems to be a promising treatment in patients with obesity presenting with non-alcoholic fatty liver disease.