The adhesion of a thin-film of PMMA to substrates consisting of Ti or Al was measured using a four-point bend technique. Initial results revealed that cracks propagated along the PMMA/metal interfaces at stable rates. Subsequent experiments showed intermittent (“stick-slip”) interfacial crack propagation consisting of cycles of crack initiation, unstable propagation, and arrest. To investigate the origin of stick-slip fracture behavior at PMMA/metal interfaces the effect of water uptake by PMMA on fracture behavior was studied. Four-point bend sandwich specimens were stored in vacuum or deionized water environments at either 25 °C or 65 °C for a period of 7 days prior to testing. The PMMA/Al system stored at 25 °C showed a transition from stable to stick-slip crack propagation when the exposure environment was changed from vacuum to water. Interface crack propagation was stable for both the PMMA/Ti and PMMA/Al systems on exposure to 65 °C water, but the critical strain energy release rate, GC was markedly reduced, indicating that water uptake promoted stick-slip fracture up to some critical degree of hydration. No change in stick-slip behavior was observed from a variation in imposed load-point displacement rate.