The natural history of asymptomatic extracranial arterial disease (EAD) was studied prospectively in 339 patients admitted for serial ultrasound Doppler examinations. Annual mortality was high at 7%, but stroke mortality was low at 0.6%: 82 patients (24%) died during the follow-up period, which lasted up to seven years (median: 29 months), only 10 from stroke but 41 from cardiac causes. The risk of suffering a stroke without premonitory transient ischaemic attacks (TIAs) was similarly low at 0.4%. Progression of EAD was the only predictor established to indicate the individual patient's cerebrovascular prognosis among a series of criteria tested (age, sex, degree and extent of carotid and/or vertebral disease, risk factors and indicators of atherosclerosis). Deterioration of EAD was observed in 108 (36%) of 296 patients by repeated Doppler examination, 174 (59%) remained constant and 14 (5%) showed an improvement. The observed low rate of strokes without premonitory TIAs is not in favour for early carotid endarterectomy in the majority of neurologically asymptomatic patients.