Diffusion-weighted magnetic resonance imaging (DWI) was carried out on a patient with Binswanger's disease suffering from acute cerebral infarction. Though an acute infarcted lesion was demonstrated as a high signal area on the T2-weighted image, it was impossible to determine whether it was acute or chronic because of extensive deep white matter lesions (periventricular hyperintensity and white matter hyperintensity lesions). However, only the acute infarcted lesion was detected on DWI which showed it as a high signal area, suggesting reduced molecular diffusion of water. The apparent diffusion coefficient (ADC), a physiological parameter that characterizes the self-diffusion on water in tissue, was lower in the acute lesion and higher in the chronic lesion. DWI can differentiate acute from chronic infarcts, which is not possible by conventional CT and MRI.