Recent reports have suggested a possible association between HIV-1 infection and "idiopathic" pulmonary hypertension (PH), but the pathogenetic role of the viral agent has not been fully defined yet. We report the cases of two white males positive for human immunodeficiency virus type 1 (HIV-1) who presented with clinical and hemodynamic diagnosis of pulmonary hypertension. They were heterosexual, non-hemophiliac, heroin abusers with no signs of clinical AIDS. Neither one of the patients had opportunistic lung infections or any other cause of secondary pulmonary hypertension. In one case, peculiar clinical and electrocardiographic features of PH were associated with signs of thrombotic thrombocytopenic purpura (TTP). The association between PH and HIV-1 infection might be explained by a severe alteration of pulmonary endothelial cell homeostasis secondary to HIV-1 viral infection.