Human immunodeficiency virus (HIV)-related pulmonary hypertension (HRPR) is a cardiovascular complication of HIV infection that has been recognized in the last years with increasing frequency. The etiology of HRPH is unknown. All the attempts to isolate HIV on pulmonary vessels in HRPH patients failed, and an indirect role for HIV in this disease has been hypothesized. Current theories on the pathogenesis focus on abnormalities of endothelial and smooth muscle cells of pulmonary vasculature. Endothelial and smooth muscle cell injury could be due to a high production or to a reduced clearance of cytokines in these patients. In fact, in several studies high levels of ET-1, IL-1alpha, IL-6 and PDGF in primary pulmonary hypertension (PPH) and in HRPH have been found. HIV gp 120 could induce the production of these cytokines by a stimulation of monocytes/macrophages. A high alpha1-adrenoreceptors stimulation of pulmonary vessels could be also implicated in the pathogenesis of HRPH. Chronic hypoxia is observed with increased frequency in HIV patients, and this could induce a chronic stimulation of alpha1-receptors of pulmonary vasculature with typical pathological changes. However, only a small percentage of HIV- patients develop HRPH. This observation suggests the existence of an idiosyncratic susceptibility to the development of vascular disease. This susceptibility could have a genetic basis, and might be determined by particular major histocompatibility complex alleles.