The clinical course of 328 patients with Buerger's disease (thromboangiitis obliterans: TAO) was followed. Neither ischaemic ulcers nor gangrene occurred in 26 per cent of the patients. Almost all of the ulcers occurred in patients between 20 and 50 years of age, with a peak incidence between 40 and 45 years. The younger the patient at the onset of the disease, the later the first ulcer occurred, and the later the first ulcer occurred, the shorter the period in which ulceration may recur. Recurrent ulcers were observed in 45 per cent of the patients. The progression of symptoms was influenced by smoking, but this was not the only deleterious factor as there were patients with stable TAO unaffected by smoking. In the 30 patients over the age of 60 years, ulceration and gangrene were not observed. In all patients, the progression of symptoms was self-limited and recurrent ulcers occurred less frequently with ageing. The rate of major amputation was low (3.9 per cent) although minor digital amputations were sometimes required. The survival rate of patients with TAO was higher than that of patients with arteriosclerosis obliterans. The aim of treatment in patients with TAO is to make patients abstain from smoking to prevent ulceration and to shorten the period of healing of trophic lesions without major amputation, as ulceration and gangrene in T AO are limited to the most distal part of the limbs, and seems to have healing potential.