Recurrent aphthous ulceration (RAU) remains a clinical problem for many patients. Efforts in prevention and/or treatment with prescription and nonprescription formulations have to date resulted in minimal success at best. A 6-month double-blind clinical study of 96 adults compared a commercially available antimicrobial mouthrinse (Listerine Antiseptic [LA], Warner-Lambert Co., Morris Plains, N.J.) and a hydroalcoholic control to evaluate the effects of vigorous twice-daily rinsing on the incidence, duration, and severity of RAU in persons prone to this disorder. LA rinse and the hydroalcoholic rinse resulted in a statistically significant reduction in the incidence of RAU occurrences from baseline. The duration of lesions and the severity of pain in subjects with ulcers during the treatment period were also significantly reduced in the LA rinse group of patients when compared with baseline. The hydroalcoholic rinse did not show a significant effect versus baseline for either severity or duration of the lesions. Rinsing therefore can be of clinical value in reducing the occurrence of RAU in susceptible patients, and LA rinse can be of significant additional value in decreasing the duration and severity of RAU.