Acute anterior uveitis is a common ocular disease characterized by inflammation of the iris and ciliary body. In the majority of patients presenting with an acute attack of anterior uveitis, the only clues to the pathogenesis of this disease are its close association with the genetic marker HLA-B27 and the likely triggering role of a variety of gram negative bacteria. HLA-B27 acute anterior uveitis appears to be a distinct clinical entity frequently associated with the seronegative arthropathies, such as ankylosing spondylitis and Reiter's syndrome. Recent advances in our understanding of the structure and function of class I HLA molecules have revealed their fundamental function in antigen presentation and this has led to a reevaluation of their role in disease predisposition.