Many patients with ischemic stroke that would benefit from ‘late’ recanalization go untreated, as current imaging-based predictions of outcome are insufficiently individualized. This study investigated whether diffusion MRI (dMRI), a standard tool in stroke diagnostics, provides additional information through effects of diffusion time dependence. Results showed elevated rates of water exchange within lesions of subacute stroke patients. The absence of such exchange appeared predictive of tissue viability in the chronic stage, even in regions normally considered irreversibly injured. Information on diffusion time dependence may thus improve penumbra definitions and help identifying subjects with favorable outcome of late recanalization.