Objective: To investigate corrosion in dental amalgam and evaluate the effects of composition and long-term aging on the alloy's corrosion behavior. Method and Materials: A sample of high-copper and low-copper formulations was employed. Corrosion tests were performed using a 3-electrode polarization cell. Anodic polarization curves were drawn, and the potential and the current density corresponding to the first anodic peak were registered. Scanning electron microscopy was performed, and the different metallurgical phases of the alloy's microstructure were examined and analyzed chemically using an energy-dispersive x-ray technique. The amalgams' corrosion behavior was evaluated at 1 week and after aging in a simulated oral environment for 6 months, 1 year, and 2 years. Data were analyzed using analysis of variance (ANOVA)/Scheffé post hoc test at a .05 significance level. Results: The potential values recorded by the high-copper amalgam were higher (P .05) than those scored by the low-copper alloy. This was attributed to the presence of a tin-mercury, g2, phase in larger quantities in the low-copper amalgam than in the high-copper alloy. For both formulations the potentials increased significantly (P .05) by about 70 mV after 2 years. This was ascribed to the gradual elimination of the corrosion-susceptible g2 phase and formation of a tin-copper, h, phase, particularly in the high-copper amalgam. Conclusion: High-copper amalgam exhibited better resistance to corrosion than the low-copper alloy. Aging in a simulated oral environment improved corrosion behavior for both high- and low-copper amalgams. Keywords: aging, anodic polarization, corrosion, high-copper amalgam, tin-copper (h) phase, tin-mercury (g2) phase