PURPOSE: To evaluate the efficacy of superselective intra-arterial fibrinolysis for acute cerebral stroke and the usefulness of pre- and postfibrinolysis diffusion-weighted MRI (DWI). MATERIALS AND METHODS: In 41 patients with acute ischemic stroke whose treatment involved intra-arterial fibri-nolysis, the occlusion site, degree of recanalization, and clinical results were compared. In 12 patients, diffusion weighted MRI was performed before fibrinolysis, and eight of these also underwent diffusion-weighted MRI after fibrinolysis. Using diffusion-weighted MRI, neurological outcomes were compared with signal intensity ratio (SIR, or the average signal intensity within the region of interest divided by that in the contralateral, nonischemic, homologous region). RESULTS: Twenty patients showed complete recanalization, nine partial recanalization, and in twelve there was no recanalization. Fourteen patients (34 %) improved neurologically. No relationship existed between occlusion sites, degree of recanalization, and clinical outcome. Among 12 patients who underwent DWI before fibrinolysis, complete recanalization was noted in eight. Neurological improvement was seen in four patients with low SIR(<1.55),while in four with high SIR(>1.7 ), neurological outcome was poor despite complete recanalization. CONCLUSION: Although superselective intra-arterial fibrinolysis for acute cerebral stroke is a good therapeutic method for recanalization, the clinical outcome can be disappointing. We therefore suggest that in cases of acute cerebral ischemic infaret, SIR-as seen on DWI-might be useful for predicting the benefits of recanalization. In such cases, further investigation of the use of DWI prior to fibrinolysis is therefore needed.