This prospective analysis of 79 patients with transient carotid ischemic attacks (TIAs) showed that only 15% of them subsequently had strokes causing serious disability or death. They were followed up from 1-9 yr. All had arteriography during initial evaluation. Most of the patients who suffered strokes had at least 1 additional risk factor for stroke, such as hypertension or a cardiac problem. Today it is probably impossible to collect data on the natural history of untreated TIAs, since virtually all patients are receiving either specific medical or surgical therapy.