An acute onset, unilateral anterior uveitis occurs during the course of either Reiter's syndrome or ankylosing spondylitis. Conversely, many patients who suffer from an acute anterior uveitis are HLA-B27-positive and have associated joint disease. The consistent presentation of the uveitis can aid in the process of differential diagnosis. This article includes a discussion of the recognition of the characteristic presentation, the complications, the role of B27 testing, the relevance of animal models, the pathogenesis, and treatment.