The studies of histocompatibility (HLA) antigens have contributed to the understanding of the pathogenesis of uveitis. Acute anterior uveitis is associated with rheumatic disorders such as ankylosing spondylitis. HLA-B 27 antigen is present in 98% of these cases. There are genetic and environmental factors influencing the activity of the disease. HLA-B 27 was found to be associated with 43% of cases of acute anterior uveitis without systemic disease. In juvenile chronic polyarthritis with acute anterior uveitis HLA-B 27 helps in differentiating between ankylosing spondylitis and Still's disease. Specific HLA antigens were also found in other forms of uveitis such as Reiter's disease (HLA-B 27), Behcet's syndrome (HLA-B 5), VKH syndrome (HLA-Bw 22J) and ocular histoplasmosis (HLA-B 7). Despite these new findings, there are still many obscure factors and further studies are required to elucidate the pathogenesis of uveitis and to achieve its prevention.