The aim of this study was to compare the marginal breakdown as a measure of clinical behavior of fillings made with two conventional amalgam alloys, one of which contained 1% stannous fluoride. Children requiring class II restorations in both mandibular molars received conventional amalgam (New True Dentalloy (R] in one molar and a fluoride-containing amalgam (Fluor Alloy (R)) in the other. Impressions of the filled teeth were taken just after polishing and at 1-yr intervals up to a 2-yr period. Plastic models were made and evaluated under a stereomicroscope. The results showed that the fluoride-containing amalgam presented slightly better margins than the conventional amalgam after 2 yr.