Accidental whole-body overexposure of radiation occurs very rarely. Radiation exposure causes DNA breaks in the cells and shows various clinical features, which are time dependent, dose dependent and tissue dependent. Neutron rays are more destructive than gamma rays but their actual effect on humans have been under-reported. We observed the time-dependent and the dose-dependent dermatological changes in a patient who was severely irradiated by neutron and gamma rays, with the aim of clarifying the clinicopathological features of severely irradiated skin. The detection of DNA breaks in keratinocytes was performed by the terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labelling technique. The degenerative changes of the skin and the re-epithelialization varied in a time dependent and dose dependent manner. DNA breaks were significantly higher in irradiated keratinocytes. Neutron rays caused depth-dependent degeneration of the skin. Evaluation of DNA breaks in the skin cells might be a clue to estimate local dosimetry.