Human immunodeficiency virus-1 infects and damages or destroys several types of cells, most importantly helper/inducer (CD4+) lymphocytes. In the majority of infected persons, the loss of CD4+ lymphocytes leads to a progressive reduction in both cell mediated and antibody mediated immunity. Early during infection most adults are asymptomatic, but after several years many develop symptoms representing a moderate degree of immune suppression. Eventually, most of these individuals become susceptible to the life-threatening opportunistic infections and cancers which define the acquired immunodeficiency syndrome. Recent advances in management, including earlier diagnosis, the use of maintenance or suppressive therapies, and specific anti-retroviral therapy with zidovudine (AZT) has nearly doubled the life expectancy for persons with AIDS. Clinical trials of new drugs, sometimes in combination with AZT, are underway. Vaccine development is proceeding, but many obstacles must be overcome before a successful vaccine can be identified.