Diffusion weighted magnetic resonance images (DWI) in hypoglycemic coma show more definite and earlier findings than do T1-weighted images, or even fluid-attenuated inversion recovery (FLAIR). However, there has been limited information on the time related changes of such MRI images. We report here the time related changes of MRI findings after prolonged hypoglycemia in a diabetic 62-year-old man without hypoxia. We found in the patient that hyperintensities in DWI, T2-weighted and FLAIR images disappeared on the 14th day along with normalization of the apparent diffusion coefficient (ADC). Single photon emission computed tomography (SPECT) showed no low perfusion findings throughout the course. Since the day when the hyperintensities disappeared, the patient became to open his eyes in response to verbal command. This paper demonstrates serial alterations in reversible DWI findings after prolonged hypoglycemia and we need to define its mechanisms in the future.