Selective IgA deficiency (IgAD) (serum IgA concentration of <0.07 g/l) is the most common primary immunodeficiency in Caucasians, with an estimated prevalence of 1/600. There are strong indications for involvement of genetic factors in development of the disease and the frequency of several extended major histocompatibility complex haplotypes (including HLA-A1, B8, DR3, DQ2) have previously been shown to be increased among Caucasian patients with IgAD.PCR was used to type HLA B, DR, and DQ alleles in 29 Iranian individuals with IgAD and 299 Swedish individuals with IgAD.The results indicate a strong association with the HLA B14, DR1 alleles in Iranian subjects and HLA B8, B12, B13, B14, B40, DR1, DR3, DR7, DQ2 and DQ5 alleles in Swedish subjects.Differences in HLA association of IgAD in Iran and Sweden confirm the notion of a genetic background of the disease and that multiple, potentially different genes within the MHC region might be involved in the pathogenesis of IgAD in different ethnic groups.