FGF21 is a novel member of the FGFs family, is mainly expressed in liver and it functions as a potent activator of glucose uptake on adipocytes. When over expressed in transgenic mice, it protects animals from diet-induced obesity and its administration to diabetic rodents and monkeys lowers blood glucose and triglyceride levels. Recently, increased levels of FGF21 have been identified as an independent risk factor related with metabolic syndrome. A review of the relevant roles of FGF21 in metabolism is presented here.