N-isopropylacrylamide (NIPAAm) hydrogels were synthesized by means of gamma irradiation, with three different methods: (a) irradiation of NIPAAm aqueous solutions; (b) irradiation of NIPAAm aqueous solution in presence of crosslinking agent N, N'-methylenebisacrylamide (BIS); and (c) in solid state, in form of disks compacted at different pressures prior to irradiation. Hydrogels of different crosslinking morphology were generated under different conditions. The hydrogels were characterized with regard to their gel content, swelling behavior in dependence on the temperature, and network properties. Morphology of the samples was characterized by SEM.