The authors report a case of subacute sclerosing panencephalitis in which the diagnosis was suggested by high b-value diffusion-weighted imaging (DWI) findings. The signal abnormalities were located asymmetrically at bilateral cerebral corticosubcortical regions. High b-value DWI showed these signal abnormalities as marked hyperintensity with decreased apparent diffusion coefficient values. The signal abnormalities were difficult to identify on other magnetic resonance imaging sequences, including routine DWI. High b-value DWI could be valuable for earlier detection of subacute sclerosing panencephalitis.