Spondylarthritis refers to a heterogeneous group of chronic diseases characterized by both axial and peripheral enthesitis, arthritis and extra articular manifestations. There is strongly linked to genetic factors and in some patients is related to clinical infections by arthritogenic bacteria. The clinical presentation and evolution are influenced by ethnicity, gender and age of onset. Ankylosing Spondylitis as a prototype of Spondylarthritis is an inherited disease with 90% of susceptibility related to genetic factors. Since the publication of the association of HLA-B*27 in the 70’s, the molecular component of this association, one of the strongest between a molecule of Major Histocompatibility Complex and disease, remains unclear. The strong association of HLA-B*27 gives to this allele a significant role in susceptibility related to disease development. Several studies have reported the association of other genes within the Major Histocompatibility Complex to susceptibility for development of the disease in others population groups.