Non-alcoholic fatty liver disease and non-alcoholic steatohepatitis, the hepatic manifestations of metabolic syndrome with close association with inzulin resistance and obesity, are the most common liver diseases, affecting up to a third of the population worldwide. They confer increased risk for hepatocellular carcinoma as well as cardiovascular diseases. The review aims to summarize advances in epidemiology, pathogenesis and clinical management of non-alcoholic fatty liver disease and non-alcoholic steatohepatitis. Besides liver biopsy and biomarkers, a novel non-invasive diagnostic tool the called “controlled attenuation parameter” measuring the attenuation of ultrasound generated by the transient elastography transducer, can quantitatively assess the hepatic fat content and differentiate between steatosis grades. At the same time, liver stiffness (fibrosis) can also be evaluated. The authors present their own results obtained with the latter procedure. In non-alcoholic fatty liver disease, the lifestyle intervention, weight loss, diet and exercise supported by cognitive behavioural therapy represent the basis of management. Components of metabolic syndrome (obesity, dyslipidaemia, diabetes and arterial hypertension) have to be treated. Although there is no approved pharmacological therapy for NASH, it seems that long lasting administration of vitamin E in association with high dose ursodeoxycholic acid may be beneficial. In addition, omega-3 polyunsaturated fatty acid substitution can also decrease liver fat, however, the optimal dose is not known yet. Further controlled clinical studies are warranted to establish the real value of any suggested treatment modalities for non-alcoholic fatty liver disease and non-alcoholic steatohepatitis, although these are in experimental phase yet. Orv. Hetil., 2013, 154, 1124–1134.