Treatments that aim to reduce the accumulation of bacteria on dental surfaces are considered today as the most efficient way of treating gingivitis and the resultant destruction of periodontal tissues. Mechanical plaque removal was found to be very effective in the control of gingival inflammation for most patients, but the supplement of toothpastes and mouthwashes with anti-plaque properties may benefit individuals with unperfected plaque control. The aim of the present study was to investigate the long-term effect of amine fluoride/stannous fluoride (AmF/SnF2) toothpaste on plaque levels and gingivitis in adults, as an additional measure to standard oral hygiene. One hundred and three adult subjects with gingivitis were divided into two randomised groups. One group used NaF toothpaste (control) and the second group AmF/SnF2 (Meridol) toothpaste. The subjects were examined every two months under double-blind conditions. The recorded parameters were plaque index (PlI), gingival index (GI) and bleeding on probing. The differences in PlI between baseline and the end of the study were statistically significant for both treatments, and no significant differences were found between the two treatment groups. There was a significant drop in GI between baseline and the concluding examination only for the AmF/SnF2 group, but the differences between the two treatment groups were not significant. A significant reduction in the percentage of bleeding sites during the six-month study period was found in the AmF/SnF2 group, but not in the control group. The results of the present study suggest that the long-term use of AmF/SnF2 toothpaste in adults may be of benefit to gingival health.