Protein tyrosine phosphatase non-receptor type 22 (PTPN22) is a strong susceptibility gene shared by many autoimmune diseases. The aim of this study was to explore the mechanisms underlying this relationship. We performed a comprehensive analysis of the association between PTPN22 polymorphism C1858T and autoimmune diseases. The results showed a remarkable pattern; PTPN22 C1858T was strongly associated with type I diabetes, rheumatoid arthritis, immune thrombocytopenia, generalized vitiligo with concomitant autoimmune diseases, idiopathic inflammatory myopathies, Graves' disease, juvenile idiopathic arthritis, myasthenia gravis, systemic lupus erythematosus, anti-neutrophil cytoplasmic antibody-associated vasculitis and Addison's disease. By contrast, PTPN22 C1858T showed a negligible association with systemic sclerosis, celiac disease, multiple sclerosis, psoriasis, ankylosing spondylitis, pemphigus vulgaris, ulcerative colitis, primary sclerosing cholangitis, primary biliary cirrhosis, Crohn's disease and acute anterior uveitis. Further analysis revealed a clear distinction between the two groups of diseases with regard to their targeted tissues: most autoimmune diseases showing an insignificant association with PTPN22 C1858T manifest in skin, the gastrointestinal tract or in immune privileged sites. These results showed that the association of PTPN22 polymorphism with autoimmune diseases depends on the localization of the affected tissue, suggesting a role of targeted organ variation in the disease manifestations.