Radiation damage in single crystal CsI(Tl) and polycrystal CsI was assessed by measuring the changes in radioluminescent intensity caused by successive neutron and gamma ray pulses from a TRIGA nuclear reactor. The radioluminescent intensity from the single crystal decreases within nine pulses by 30% in the near infrared range (0.7–4.5 μm) and by 25% in the visible range (0.2–1 μm) before staying constant. For the polycrystal CsI, the emission in the visible range decreases by 60% within 6 pulses and then remains constant, whereas no measurable emission is observed in the infrared. Finally, a heating and cooling cycle is shown to repair the damage for both crystals.