Both environmental and genetic factors play a role in the pathogenesis of obesity. At present, researchers are examining the genetic background of overweight. Over 100 genes are suspected to influence the obesity. One of those genes is FTO (fat mass and obesity-associated gene). In the manuscript, the relationship between FTO gene polymorphism (AA allele) and overweight, obesity and their consequences are discussed. It was proved, in studies on large number of people, that FTO gene polymorphism is related to higher body mass index, weight and abdominal circumference. Some authors showed that FTO gene polymorphism influences the food intake, energy expanditure and insulin resistance. The expression of FTO gene product was noticed in both, the peripheral as well as central nervous system (hypothalamus). It is possible that FTO gene product is involved in the DNA and RNA reparation and other metabolic processes, however, its function is not yet clear. The assessment of FTO gene polymorphism can allow us to separate patients with the tendency for higher weight. The elucidation of the role of FTO in the pathogenesis of obesity can result in the development of new therapeutic options for this epidemic of XXI century.