PURPOSE: To investigate the findings of diffusion-weighted MR imaging in patients with transient ischemic at-tacks (TIA). MATERIALS AND METHODS: Between August 1996 and June 1999, 41 TIA patients [M:F = 28:13, mean age 57 (range, 27 -75) years] with neurologic symptoms lasting less than 24 hours underwent diffusion-weighted MR imaging. The time interval between the onset of symptoms and MR examination was less than one week in 29 patients, from one week to one month in eight, and undetermined in four. Conventional MR and DWI were compared in terms of location of infarction and lesion size (<1 cm, 1 -3 cm, >3 cm), and we also determined the anatomical vascular territory of acute stroke lesions and possible etiologic mechanisms. RESULTS: The findings of DWI were normal in 24/41 patients (58.5%), while 15 (36.6%) showed acute ischemic lesions. The other two showed old lacunar infarcts. All acute and old DWI lesions were revealed by conven-tional MR imaging. Among the 15 acute stroke patients, seven had small vessel lacunar disease. In three pa-tients, the infarction was less than 1 cm in size. Six patients showed large vessel infarction in the territory of the MCA, PCA, and PICA; the size of this was less than 1 cm in three patients, 1 -3 cm in two, and more than 3 cm in one. In two patients, embolic infarction of cardiac origin in the territory of the MCA and AICA was diagnosed. CONCLUSION: The possible mechanism of TIA is still undetermined, but acute lesions revealed by DWI in TIA patients tend, in any case, to be small and multiple.