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There has been substantial progress in our understanding of the pathogenesis and clinical consequences of infection with HIV since the virus was first identified more than 20 years ago. The details of the viral replication cycle are increasingly better understood as are the identification of host elements that both regulate viral replication and are necessary for it. Greater understanding of these events has resulted in the development of therapies for HIV infection and as a consequence there has been a dramatic improvement in overall survival in the era of HAART. With this improvement in survival has come an increasing recognition of the importance of many long-term sequelae of subclinical immune deficiency and the attendant immune activation that characterize HIV infection. One complication of chronic HIV infection for which the pathogenesis is obscure is pulmonary arterial hypertension (PAH). Cases of HIV-related PAH (PAH–HIV) have been recognized with increasing frequency in recent years. Although it is likely that PAH–HIV has an underlying etiology specifically related to HIV infection, it shares several key clinical and pathological similarities with other forms of PAH. This article outlines the features, classification and treatment of PAH, and recent theories about the underlying etiology of the disease. We will also discuss the occurrence of PAH in HIV infection and propose some hypotheses regarding pathogenesis that will be covered in more detail in the accompanying articles in this supplement.