The ability of Tinuvin 622, a Hindered Amine Stabilizer (HAS), in decreasing of radiation damage to commercial PMMA matrix used in manufacturing of medical supplies was examined. Effects of gamma irradiation in PMMA specimens irradiated at dose range of 10-60 kGy were assessed by comparison of the variation of viscosity average molar mass (M-nu) of PMMA with Tinuvin 622 (PMMA-622) when compared with PMMA without the additive (PMMA-control). Samples containing Tinuvin 622 presented smaller decrease of M-nu as a function of dose. This phenomenon causes direct influence in the mechanical properties of PMMA. Above 10 kGy, both PMMA-control and PMMA-622 undergo changes in the yellowness index with increase of absorbed dose; however, the phenomenon was less pronounced for PMMA-622 samples. Electron Spin Resonance spectra showed that Tinuvin 622 induces a faster evolution of radicals formed in PMMA radiolysis followed by a decrease in radiation-induced degradation of the samples. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 116: 748-753, 2010