Non-alcoholic fatty liver disease is present in 15-25% of the general population. The fundamental derangement in non-alcoholic fatty liver disease is insulin resistance, a key component of the metabolic syndrome, which includes type 2 diabetes mellitus, dyslipidemia, hypertension, and obesity. The natural history of non-alcoholic fatty liver disease is not always benign, and causality for chronic liver disease and cirrhosis is well known in clinical practice and sometimes it is accompanied by hepatocellular carcinoma. Non-alcoholic fatty liver disease is likely to be associated with increased cardiovascular disease risk, and it raises the possibility that non-alcoholic fatty liver disease may be not only a marker but also an early mediator of atherosclerosis. Therapy is currently directed at treating components of the metabolic syndrome which may be beneficial also for the liver.