The epidemic of pediatric acquired immunodeficiency syndrome (AIDS) in the United States, which peaked during the mid-1980s and early 1990s, was characterized by a variety of opportunistic infections in children infected with human immunodeficiency virus (HIV), often as the presenting illness of their HIV infection. Pneumocystis carinii pneumonia (PCP) during infancy was responsible for significant morbidity and mortality, followed by many other opportunistic infections, including recurrent, serious bacterial infections; disseminated cytomegalovirus infection; and disseminated Mycobacterium avium complex (MAC) infection. Many of these infections involve the lower respiratory tract either as a primary site of infection or as one of the sites involved in disseminated disease. Since the mid- to late 1990s, the pediatric HIV epidemic in the United States has witnessed a dramatic decrease in the frequency of most opportunistic infections and other severe manifestations of HIV infection in children, primarily because of lower rates of mother-to-child HIV transmission, development and implementation of guidelines for PCP prophylaxis, and availability of highly active antiretroviral therapy. Far fewer children are at risk for clinical progression of HIV disease and for opportunistic infections. Despite these successful trends, pulmonary opportunistic infections and pulmonary disease remain common clinical manifestations of pediatric HIV disease.