Background and Purpose— Several stroke risk scores for prediction of functional outcome have been developed, but rarely validated in Asian populations. We assessed the validity of the iScore, recently developed from Canadian stroke population, in an Asian stroke population from Korea. Methods— We applied the iScore to 4061 eligible participants with acute ischemic stroke in the nationwide multicenter stroke registry in Korea. The main outcome was poor functional outcome defined as having a modified Rankin Scale 3 to 6 at 3 months after stroke onset. The secondary outcome was death at 3 months. C-statistics were calculated to assess performance of the iScore. Results— Poor functional outcome was found in 1496 patients (36.8%), whereas death at 3 months occurred in 294 patients (7.2%). C-statistics were 0.819 (95% confidence interval, 0.805–0.833) for poor functional outcome and 0.861 (95% confidence interval, 0.840–0.883) for death. Overall, there was a high correlation between observed and expected outcomes for poor functional outcome (Pearson correlation coefficient, r =0.990) and for death ( r =0.969) according to risk score. Conclusions— The iScore reliably predicts poor functional outcome or death at 3 months after stroke in Korean patients.