Our knowledge of the genetics of insulin dependent diabetes (IDDM), and in particular the HLA system, has gained considerable expansion thanks to the application of molecular biology. The genetic susceptibility to the disease is linked to the HLA region, particularly at DQ-alpha and DQ-beta chain genes. Particular amino acid other than aspartic acid in position 57 of the DQ beta chain and the presence of an arginine in position 52 of the DQ alpha chain and to how these markers can be used to identify subjects at risk for developing IDDM. The identification of such subjects may be useful for the development of strategies aimed to prevent the disease and in addition may offer a new insight into population screening.