In an era when heart-lung transplantation offers a therapeutic option for patients with Eisenmenger's syndrome, it is important to assess the natural history of this condition. With this objective the authors studied 62 patients followed-up by the same cardiologist. The average follow-up period was 16 years, but 22 patients were followed up for over 20 years. The average age at death was 29 years. It differed significantly for genetically normal patients (31 years for 21 fatalities) compared with a population of trisomics (21 years for 6 fatalities). Half the patient population lived for over 30 years. Fourteen of the 27 deaths occurred during the third decade and only 4 before the age of 20. The probability of surviving 10 more years for a 20 years old genetically normal patient was 56%. The causes of death in the 19 cases in which it could be established were: 5 sudden deaths, 4 right heart failures, 3 massive haemoptyses, 3 pulmonary emboli, 2 pneumonias and 2 peroperative deaths. The functional disability was nearly always minimal or mild, enabling the patient to work: 24 of the 45 non-trisomic patients had full-time jobs. Pregnancy was a poor prognosis factor and could be lethal (2 deaths due to pulmonary embolism in the post-partum period). A heart-lung transplantation would only seem to be justified in patients with severe symptoms, polycythaemia, irreversible right heart failure and/or haemoptysis.