Severe pulmonary hypertension presenting as acute cor pulmonare was observed in a HIV positive heroin addict. The usual aetiological investigations were negative. The apparently primary pulmonary hypertension was resistant oxygen and vasodilator therapy and was fatal in 6 months. Anatomopathological examination revealed the presence of talc microemboli in the pulmonary arterioles, severe medial hypertrophy and fibrous subendothelial thickening. The presence of the talc suggests that the pulmonary hypertension in this case was due to obstruction of the pulmonary vascular bed by the obstructive arterial lesions, despite the context of HIV infection.