The beta3-adrenergic receptor (beta3-AR) may play a key role in the regulation of lipid metabolism and glucose homeostasis. Adrenaline and noradrenaline beta3-AR stimulate lipolysis and thermogenesis in human fat cells and increase glucose uptake in skeletal muscle. Therefore, the beta3-AR gene may be associated with obesity and related diseases, such as type 2 diabetes, coronary heart disease and hypertension. Many studies in different ethnic groups showed an association of beta3-AR gene polymorphism with insulin resistance, obesity and its metabolic disorders such as type 2 diabetes, coronary heart disease and hypertension. A Trp64Arg mutation in the beta3-AR gene has been reported to be correlated with the occurrence of those disorders among obese. Several studies revealed also the influence of the Trp/Arg polymorphism on carcinogenesis and its contribution to the link between cancer and obesity. Since obesity is a serious problem as a civilization-related disease, it is very important to investigate genes suspected to be connected with it.