The clinical, biochemical and prognostic characteristics of 37 patients with Wegener's granulomatosis were studied in relation to age. Eleven patients were older than 60 years when the first sign of the disease appeared. Except for the fact that the renal lesions seemed to be more severe in these patients, there was no significant clinical or biochemical difference between them and patients under 60. Five patients over 60 years of age died during the first 2 years of Wegener's granulomatosis. Death was due to infection in 3 cases, to acute renal failure as complication of intra-alveolar haemorrhage in 1 case and to metastatic cancer in 1 case. Age-related comparisons of survival rates showed that the probability of surviving was lower in elderly subjects: 78 per cent at 1 year and 39 per cent at 3 and 5 years, as opposed to 96 per cent at 1 and 3 years and 84 per cent at 5 years in younger subjects (P less than 0.01). This poor prognosis is probably due to the renal lesions which constitute an important cause of death in the published series. Rapidly progressive glomerulonephritis being amenable to an early and intensive treatment, elderly patients should be treated as energetically as younger patients.