It is accepted that lifestyle and environmental factors have an important influence on obesity. However, susceptibility to obesity is determined by genetic factors. In the presence of a genetic predisposition to obesity, the severity of the disease is largely determined by environmental factors. Although they are not frequent, single gene mutations are also known to cause obesity. The discovery of leptin in 1994 has profoundly changed our understanding of obesity. We now know that there is a physiological system involved in maintaining weight. Arcuate nucleus of the hypothalamus is the appetite control center of the body and several hormones are now known to influence this center. An understanding of the genes causing obesity and of their interaction with each other will be useful in the development of a therapy in obesity. Anahtar Kelimeler : obesity, genetics,obesite, genetik