Radiologic assessment of acute transient ischemic attacks (TIAs) has been handicapped by the low sensitivity of CT and conventional MR imaging for acute small-vessel infarction and the difficulty in differentiating between acute and chronic lesions by use of these methods. Our purpose was to evaluate the incidence of TIA-related infarction by using diffusion-weighted MR imaging to determine whether the presence of a diffusion imaging abnormality correlates with the duration of symptoms or cause of TIA.