The hydrolytic aging of an unstabilized industrial sample of polycarbonate was studied at 40, 70, 80, and 90-degrees-C, 100% RH. The water absorption characteristics show that, at equilibrium, the polymer absorbs about 0.04 mol water per ester group and that the equilibrium is reached after about 10-40 h exposure, i.e., far before irreversible changes of physical properties are observed. Differential scanning calorimetry reveals the combined effects of hydrolytic chain scission and physical aging on glass transition temperature. Investigations on tensile yield properties showed that hydrolytic chain scission leads to a significant decrease of the apparent Eyring’s activation volume. These observations strongly support the hypothesis that there are preexisting or hydrolysis-induced defects responsible for an heterogeneous distribution of chain scissions that would be concentrated into localized microdomains.