The aims of this study were to assess the effects of sterilization with gamma-irradiation on (i). bulk cladribine and (ii). cladribine-containing biodegradable copolymers. The stability of cladribine upon irradiation was confirmed by TLC, HPLC, UV, IR, DSC, rentgenography and electron microscopy. The stability of copolymers containing cladribine upon irradiation was assessed by IR, DSC and EPR. In vitro kinetics of nucleoside release from the copolymers before and after irradiation were compared, and only slight changes were found. Results of our study indicate that gamma-irradiation can be safely applied for the sterilization of cladribine or cladribine-containing copolymers for medical purposes.