Samples of PAAHI, a cross-linked polymer belonging to the family of poly(amidoamine)s, were investigated at different hydration levels by means of C-13 and H-1 NMR techniques in order to obtain information on water/polymer interactions. Carbonyl oxygens and amine nitrogens were identified as the main sites of interaction giving hydrogen bonding with water molecules. The polymer turned out to be uniformly plasticized already at moderate degrees of swelling. The hydration process was found to occur in a stepwise manner, with the first batch of water saturating a hydration layer and additional water filling the polymer meshes. The proportion of water in the different states was quantitatively determined.