Triclosan, an antibacterial agent introduced in toothpastes and mouthrinses, has recently been shown to have anti-inflammatory and analgesic properties. The aim of the present double-blind cross-over study was to examine the effect of triclosan on the incidence of recurrent aphthous ulceration (RAU) when administered in mouthrinses. The study included 30 patients with a history of multiple recurrent aphthous ulcers. Three different triclosan-containing mouthrinses, differing only in their solubilizing agents were used and compared with a control rinse. The number of new ulcers, ulcer-free days and the severity of pain were recorded. The results showed that the patients experienced a significant decrease in the number of oral ulcers during the experimental period when the mouthrinses contained triclosan. It may thus be concluded that triclosan has the potential to reduce the number of aphthous ulcers presumably due to its anti-inflammatory properties.