Fourteen Cu-rich and 4 conventional amalgam restorations were recovered from a clinical study. All restorations had full clinical documentation from placement until removal and had been in service between 3 and 10 years. All had marginal deterioration ratings of 3 based on a photographic scale which ranged from 1–6. Microstructural studies of buccolingual cross-sections of the Cu-rich restorations showed marked variability in corrosion products, porosity and phase contents. Corrosion product content was highest near the peripheries of the restorations and decreased with distance from the interfaces. Internal corrosion products did not appear to be correlated with the age of the restoration. The major corrosion products found in all samples appeared to be tin oxides and tin hydroxychloride regardless of the type of amalgam. In addition to the tin containing corrosion products In containing products were found in the In containing amalgam. Zn-containing amalgams frequently formed a thick Zn-containing layer at tooth-amalgam interfaces as a result of clinical use. The Zn-rich layer resulted from corrosion of the amalgams since no Zn-containing bases were used in this study. The Ag-Hg matrix of the amalgams was also altered, most notably by the transformation of gamma one to beta one and by the formation of Sn-rich corrosion products along matrix grain boundaries. It is apparent from this study that amalgam restorations with the same moderate clinical status exhibited significant microstructural alterations, but no single characteristic could be correlated with the clinical rating.