Multiangle laser light scattering (MALLS) is used to monitor changes in molecular weight during solid state aging of polyamide-11 (PA-11). A mathematical model is presented which successfully describes the degradation kinetics of PA-11 in pH 7 water. The MALLS results demonstrate that there is a recombination reaction in the solid state, which may be described as a cage effect during hydrolysis-degradation of the amide bond. During aging, the competing recombination and hydrolysis reactions lead to the formation of an equilibrium molecular weight. The equilibrium molecular weight is surprisingly high at about 26 000 in pH 7 water, a value close to the ductile-brittle transition, The activation energy of hydrolysis is 81 to 87 k.J/mol, close to the values of previous acid degradation studies and a recent value of 96 kJ/mol for hydrolysis of the peptide amide bond.