The production of defects by thermal neutrons in CdS results from the recoil of an energetic 114Cd nucleus. The recoil results from prompt emission of 9 MeV of gamma energy following thermal-neutron capture by 113Cd through the nuclear reaction: 113Cd + nth → (114Cd) → 114Cd + γ. The changes in the optical and electrical properties of CdS were measured to determine the effect of such recoils. A recombination center for the 7200A emission is produced and both the 4880A emission and edge emission are reduced. In addition, the conductivity of initially conducting CdS crystals is decreased by many orders of magnitude. The temperature dependence of the conductivity of thermal-neutron irradiated crystals indicates the production of a state about 0.5 eV below the conduction band.