Infection with the human immunodeficiency virus (HIV) is associated with the development of psoriasis and related disorders, including psoriatic arthritis, dactylitis and enthesitis, and Reiter's syndrome. The etiologic mechanisms remain unclear but most likely represent a combination of genetic and environmental factors. Therapy for these diseases in the setting of HIV infection is often difficult not only because of their characteristically increased severity, but also because the use of conventionally effective immunosuppressive agents may be counterproductive in this patient population.