The marginal degradation and corrosion of restorations made of a high copper dispersed amalgam were studied as a function of time for up to 5-yr observation periods. The effect of minor defects present after finishing the restorations was included in the assessment of the initial marginal degradation. A slow progressive marginal degradation was noted and it was enhanced by initial defects. Subsurface corrosion including attacks of the phase and grain boundaries, corrosion within the bulk, and layers of corrosion products along the tooth/restoration interfaces were observed in restorations after some years in clinical service. The subsurface corrosion is considered to weaken the amalgam and it might enhance the marginal degradation, i.e. a stress corrosion type of degradation.