To clarify the clinical significance of diffusion-weighted magnetic resonance imaging (DWI) hyperintensity in acute cerebral ischemia, 34 patients were investigated with cerebral ischemia that had lasted no more than 8 hours. Either a spin echo sequence with navigator echo (n = 21) or an echo planar sequence (n = 13) was used for DWI using 1.5 tesla magnet. The eventual infarction was judged from T2-weighted image (T2 WI) or CT performed 2-12 days after the onset and was classified into cortical (n = 24) or perforating artery (n = 10) area. The eventual infarction was compared in size with the acute DWI finding and expressed as larger, same or smaller. Thirty patients showed ischemic hyperintensity lesions on acute DWI (6 patients on T2 WI). In cortical artery areas, the eventual infarction was same as hyperintensity area of acute DWI in 15 cases, larger in 8 cases, smaller in 2 cases. In perforating artery areas, the eventual infarction was same as hyperintensity area of acute DWI in 8 cases, and larger in 2 cases. These results suggest that in the perforating artery areas, the acute DWI hyperintensity is a good predictor of the eventual infarction and that in cortical artery areas, dynamic ischemic process may continue for hours before resulting in the eventual infarction.