Non alcoholic fatty liver disease (NAFLD) has been recognized as a hepatic manifestation of systemic metabolic disease associated with insulin resistance. Recent studies have reported that NAFLD is related with various systemic complications such as cardiovascular, renal, metabolic disease independent of obesity, other component of metabolic syndrome (MetS). Thus, NAFLD should be newly regarded as an early mediator of systemic metabolic disease as well as liver specific disease. The mechanisms of adverse effect of NAFLD on other medical diseases are not fully understood, so further study is needed for understanding and future management strategies of NAFLD. (Korean J Med 76:25-29, 2009)