The electromagnetic calorimeter of the Gamma-Ray Large Area Space Telescope (GLAST) consists of 16 towers of CsI(Tl) crystals. Each tower contains 8 layers of crystals (each 326.0x26.7x19.9 mm3) arranged in a hodoscopic fashion. The crystals are read out at both ends with photodiodes. Crystals produced by Amcrys-H (Ukraine) are used. A full size crystal was irradiated with a 180 MeV proton beam and the radiation induced attenuation was measured. The induced radioactivity of the crystal was also studied. In this paper we will discuss the damage due to proton irradiation and compare this with the expected in-orbit background flux.