Opportunistic infections ultimately occur in most patients infected with human immunodeficiency virus (HIV) and are responsible for 90% ofdeaths. Over the decade since the acquired immunodeficiency syndrome (AIDS) was first recognized, important advances have been made in reducing the morbidity and mortality of opportunistic infections in patients infected with HIV. These include an improved understanding of the relationship between immunologic parameters and infection, allowing the occurrence of infectious complications to be more predictable; development of prophylactic regimens and chronic suppressive regimens that are effective, well tolerated, and convenient;and emphasis on earlier diagnosisand therapeutic intervention of those infectious processes that are not prevented. These advances have allowed the quality and duration of patient survival to improve during this decade, but they can also be anticipated to alter the spectrum of clinical manifestations that health care providers are going to see during this epidemic's second decade.