There was an epidemic of chronic pulmonary hypertension in Austria, the Federal Republic of Germany and Switzerland, starting in 1967, peaking in 1968/69, and disappearing after 1972. The mechanism leading to pulmonary hypertension was chronic precapillary vascular obstruction due to plexogenic pulmonary arteriopathy. There was a close geographic as well as temporal relation of the epidemic to the marketing and intake of the appetite depressing drug aminorex fumarate (Menocil). 10 years after the epidemic, half of the patients have died, usually of right heart failure. Of those surviving, half present a definite regression of the pulmonary vascular obstruction. Average survival after the initial diagnosis was 3.5 years in those patients who died. Their PA pressure (+22%) and pulmonary arteriolar resistance (+40%) was higher at the onset of the observation period if compared with the corresponding values of the survivors; also the incidence of right heart failure was significantly higher (84 vs. 58%). Among the surviving patients, the only difference between those with an improved and those with a worsened haemodynamic situation was the age at the beginning of the weight-reducing treatment, those with a progression being 10 years older. The probability of survival after 10 years is considerably higher in chronic pulmonary hypertension of vascular origin (CPHVO) after aminorex than in "classical" primary pulmonary hypertension (CPHVO of unknown cause) and in CPHVO due to recurrent silent pulmonary thromboembolism. This difference in prognosis is an argument in favour of the identity of chronic pulmonary hypertension developing after the intake of the appetite depressing drug aminorex.