The natural history of aortoarteritis was studied in 88 patients (54 women and 34 men). The average age was 24.0 +/- 8.8 years at onset of symptoms and 28.3 +/- 9.9 years at diagnosis. The follow-up period was 83.6 +/- 74.4 months from onset and 33.2 +/- 37.0 months from diagnosis. Ten patients (11.4%) died during follow-up (0.016 deaths/patient year), and 22 patients (25%) suffered major nonfatal events (0.042 events/patient year). The cumulative survival at 5 and 10 years after the onset was 91.0 +/- 3.3% and 84.0 +/- 5.6% (mean +/- SEM), respectively. The event-free survival rates at the same intervals after onset were 74.9 +/- 5.0% and 64.0 +/- 7.4%, respectively. The overall survival and event-free survival at 10 years after diagnosis was 80.3 +/- 6.5% and 61.6 +/- 7.5%, respectively. Patients with no complications or a mild single complication at diagnosis had a higher event-free survival rate than those with severe single complication or multiple complications at 5 years--97.0 +/- 2.9% and 59.7 +/- 7.3%, respectively (p less than 0.001). Severe hypertension (p less than 0.01), severe functional disability (p less than 0.01), and evidence of cardiac involvement (p less than 0.05) were good predictors of either death or major event on follow-up. These data are useful in making an objective assessment of the prognosis and in planning elective interventions.