Objective: The purpose of this study was to compare the marginal and internal adaptation of a non-gamma-2 amalgam and an ultrafine compact-filled light-cured composite in small to moderate-sized Class II restorations of conventional design. Method and materials: Fifty recently extracted human premolar and permanent molar teeth were selected for the study. The teeth were restored with either a non-gamma-2 amalgam alloy or a light-cured resin composite. The marginal adaptation of the restorative materials to the proximal surface outline form of each preparation was assessed. The mean percentages of perfect margins, marginal fissuring, and underfilled margins for the 2 restorative materials were recorded and statistically analyzed. Results: Both materials performed equally well in the buccal and lingual segments of the proximal box. At the cervical margin, the resin composite restorations showed a significantly greater number of imperfect margins and marginal fissuring. The incidence of underfilled margins was low for both restorative materials even at the cervical margin. Conclusion: Although there was some cause for concern about the marginal adaptation of the resin composite restorations along the cervical margin, the findings support contemporary teaching that small to moderately sized conventional Class II preparations may justifiably be restored with an appropriate resin composite.