Viral infections, in general, and retroviral infections, in particular, have been considered possible etiologic agents of a variety of disorders, including cancer; immunodeficiency; central nervous system disorders, such as multiple sclerosis; and autoimmune disorders, such as polymyositis, arthritis, Sjögren's syndrome, and glomerulonephritis. The current pandemia of HIV-AIDS and its associated opportunistic non–HIV infections, that is, parvovirus B19, hepatitis C virus, and herpes virus, has renewed interest in the possible role of viruses in immune-mediated disorders. From the onset of the HIV epidemic until July 1996, approximately 21.8 million adults and children worldwide were infected with HIV, and of this total, 94% were living in the developing world, with 19 million adults and children living in sub-Saharan Africa and in south and southeast Asia. In the United States approximately 750,000 to 1.5 million people have been infected. By July 1996, an estimated 5.8 million people had died from AIDS. 3 Most infections in adults have been transmitted during unprotected sexual intercourse, comprising over 70% of cases. Recent reports, however, suggest that the incidence of HIV infection may be decreasing in the United States, particularly among certain populations. 74 Over the past year, important advances in HIV pathogenesis, the use of viral load as a prognostic and therapeutic tool, and the development of newer antiretroviral therapeutic strategies have been beneficial for early detection and treatment. Still, effective prevention strategies need to be implemented to obtain a decrease in the incidence of infection. Infection with HIV is associated with a wide spectrum of clinical presentations that ranges from the asymptomatic state to AIDS. Recently, the importance of recognition of the acute retroviral syndrome has received emphasis because it provides the opportunity of prompt institution of appropriate therapy 89,122 ; this acute retroviral stage begins after initial exposure and is characterized by the development of an HIV–specific antibody response, high levels of viremia with immunologic activation, decline in CD4+ cell counts, inversion of CD4+:CD8+ ratio, and further absolute increase of CD8+ lymphocytes. Symptoms develop within 5 to 30 days post exposure and seroconversion occurs from 1 to 10 weeks after the acute illness, leading to the second phase of the disease in which the amount of viremia declines, eventually reaching a “set point” and generation of HIV–specific antibody response. The third phase is characterized by a marked decline in the number of CD4+ T lymphocytes, increase in the levels of circulating virus and infected cells, and the appearance of the multitude of symptoms characteristic of AIDS. Musculoskeletal manifestations can occur at any phase of the infection, although they are much more prevalent in the late phase. These manifestations include a variety of well-defined disorders from isolated symptoms like arthralgias and myalgias to distinct rheumatic disorders, including Reiter's syndrome or polymyositis.