Resistin is a 12.5-kDa polypeptide hormone produced by adipocytes and immunocompetent cells. It was originally proposed as a link between obesity and insulin resistance/diabetes. Later, studies revealed that substantial inter-species differences exist between the major sites of resistin production in rodents (adipocytes) and humans (immunocompetent cells). While in rodents resistin appears to have an important role in the development of liver insulin resistance, its role in humans is less clear, and it is probably involved in the regulation of inflammatory processes rather than in insulin sensitivity. Current experimental and clinical data concerning resistin physiology and pathophysiology, and its possible role in the development of insulin resistance and atherosclerosis are detailed in this review.