This article reviews the ophthalmological significance of the association between HLA-B27 and acute anterior uveitis (AAU). HLA-B27 determination should be performed in all cases of acute anterior uveitis (AAU), since B27+AAU is a distinct kind of uveitis. All B27+AAU patients have to be referred to a rheumatologist because half of these patients has ankylosing spondylitis or Reiter's syndrome. The structure and physiological role of HLA-class I molecules is now known. It is probable that the role of HLA-B27 in the pathogenesis of AAU will be revealed in the coming years.