Type 2 diabetes mellitus is a complex disease whose clinical phenotype results from the variable combination of genetic and nongenetic factors. The aim of the present study is to investigate the network linking phenotypes and genotypes in patients with newly diagnosed type 2 diabetes mellitus. In selected cases, in which clinical evidence hints at possible monogenic basis of the disease, the genotype and the phenotype of relatives also will be assessed to elucidate further the etiology of the disease.