Non-alcoholic fatty liver represents one of the most frequent liver diseases, affec-ting 25 to 30% of the world population. While its pure steatotic form is usually benign, its active form, called non-alcoholic steatohepatitis (NASH), exposes the risk of cirrhosis and, even in the absence of cirrhosis, of hepatocellular carcinoma. This disease is related to an excess of hepatocyte free fatty acids mainly of acquired origin (overnutrition in carbohydrates and fats, sedentary lifestyle). This excess produces lipotoxic compounds that generate inflam-mation and hepatic fibrosis. Diagnosis is based primarily on a non-invasive approach (namely without resorting to liver biopsy), combining clinical, biological, and imaging data. Steatosis is confirmed by ultrasound or, better, by coefficient attenuation parameter (CAP) associated with the FibroScan & REG;. The assessment of fibrogenic impact should be done, in the first line, by the FIB-4 test (based on age, transaminases and platelets), possibly completed by the Fibro-meter or the Fibrotest, and/or by elastometry based on mechanical (FibroScan & REG;) or acoustic (ARFI) impulse. Magnetic resonance elastometry is a powerful but less accessible technique. To date, treatment remains above all preventive, based on hygienic and dietary measures. Multiple pharmacological approaches are promising but have not yet been officially approved. In case of morbid obesity, bariatric surgery has a favorable effect on the non-alcoholic fatty liver. Hepatic transplantation has similar results to those obtained in other hepatopathies but requires considering the risks related to the metabolic context.& COPY; 2023 l'Academie nationale de medecine. Published by Elsevier Masson SAS. All rights reserved.