The swellability and mass loss of poly(vinyl alcohol)-graft-[poly(rac-lactide)/poly(rac-lactide-co-glycolide)] hydrogels upon hydrolysis are strongly affected by the composition of the hydrogels. Hydrophobic hydrogels remain at a relatively constant mass for a couple of weeks, and the mass decreases dramatically thereafter, whereas more hydrophilic hydrogels lose mass right from the beginning. All hydrogels display water uptake values between 90 and 280% within 8 weeks. For longer periods of degradation, the water uptake increases up to a maximum of about 900%. Studies of the thermal properties of samples upon degradation and their IR measurements have shown that the degradation rate is related to the physical and chemical structure of the hydrogels and hence to the hydrophobic/hydrophilic balance; that is, the degradation increases with the increasing hydrophilicity of the material. As a result, degradation can be engineered through the variation of the composition and structure of the material. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 112:1538-1545, 2009