We investigated the clinical outcomes and the progression of the internal carotid arterial lesions of a group of patients presenting with hemispheric TIAs. The cumulative frequency of TIAs during a mean follow-up period of 40 +/- 14 months was 14%, and no relationship was found between new TIAs and the presence of known cardiovascular risk factors or plaque characteristics as determined by duplex scanning. With the exception of one patient who died of stroke, none of the patients developed a permanent neurologic deficit. The cumulative death rate was 6.5%; myocardial infarction was the most common cause (3 out of 7). Anatomic progression of plaques was determined by duplex scanning in 22% of the internal carotid arteries. No relationship between progression of these plaques and the development of new TIAs was evident. We conclude that, in this group of patients, TIAs do not inevitably lead to stroke and that TIAs are not predictable based on risk factors or plaques characteristics.