There are insufficient data available on the epidemiology of fatty liver to design a complete and correct view of the prevalence, incidence and natural history of this disorder. This article, mainly based on the revision of recently published papers in this field, attempts to give an overview of the current findings on the epidemiology of fatty liver worldwide. The possible factors involved in the development of fat accumulation in the liver, and their potential role in the progression of the disorder will be also addressed.