The records of 43 patients older than 18 years presenting with tetralogy of Fallot were retrospectively examined to determine the semiological characteristics of the disease in adults. One or more palliative operations had previously been performed in 27 patients. Full correction was carried out in 38 patients with results described below. Tetralogy of Fallot has the following characteristics in adults as compared with children: clinically, heart failure, attacks of angina, haemoptysis and sequelae of previous complications are more frequent; at electrocardiography, right atrial hypertrophy, right bundle disorders of conduction and ventricular extrasystoles are also more frequent; radiology shows that cardiomegaly is no longer exceptional; haemodynamic studies demonstrate an increase in right atrial and right ventricular end-diastolic pressures. These characteristics indicate a deterioration of haemodynamic adjustment to the disease with age. The operative morbidity mostly consisted of haemorrhages (55% of the patients), more frequent in subjects with permeable anastomoses (p less than 0.01), and heart failure (50% of the patients) the frequency of which increased with the subject's age, the duration of the operation and the use of an infundibulo-pulmonary prosthesis (p less than 0.05). The operative mortality (18%) depended on the extent of the pulmonary stenosis and on the presence of a previous anastomosis (p = 0.04). An analysis of the causes of death reported in the literature showed that in adults the presence of an anastomosis constitutes a separate risk factor in complete repair. The excellent long-term results of corrective surgery concerning cardiac function and survival suggest that except for those rare cases where the operative risk is very high all adults with tetralogy of Fallot should undergo complete repair.