Non alcoholic fatty liver disease (NAFLD) and its more agressive form, non alcoholic steatohepatitis (NASH) are entities that are becoming subject of interest of the medical community in general, especially because of the increased prevalence of diabetes and obesity in the world population. There is solid evidence linking NAFLD with the so called metabolic syndrome or syndrome X, to the point of accepting hepatic steatosis and its spectrum as one more element of the latter, along with diabetes, hipertension, hypertriglyceridemia and obesity. Insulin resistance seems to be the common link between these entities. Clinical evaluation of every patient with abnormal aminotransferase levels should take into account non alcoholic fatty liver and its spectrum, especially if the subject is obese or diabetic. Despite the important developments in the field of imaging, currenty the only way to differentiate NASH from simple NAFLD is by performing a liver biopsy, which should be discussed extensively with the patient. The prognosis of simple NAFLD is generally benign, but if there is fibrosis, ballooning of the hepatocytes, inflammation and Mallory bodies there is risk to progression to cirrhosis. Liver histology in NAFLD is indistinguishable from alcoholic hepatitis, although the clinical course is generally more benign. Despite this long and protracted clinical course, an important number of subjects have complications of cirrhosis including hepatocellular carcinoma, and many patients require a liver transplantation. There is no specific treatment for this condition, although every therapeutic regimen should include a gradual and supervised weight reduction, a balanced diet and exercise, as well as correction of precipitant factors. There is currently no specific pharmacologic treatment for NASH or NAFLD. Current body of evidence and some pilot studies suggest that the future might be concentrated in agents improving insulin resistance. Meanwhile, we should do our best to study the prevalence of NAFLD in our country and, when clinically pertinent, study histologically those patients with high risk of fibrosis.