A double-blind placebo controlled trial of 5% 5-aminosalicylic acid (5-ASA) cream for the treatment of oral aphthous ulcers was carried out on 22 subjects. The cream or a placebo (11 patients each) was applied to the ulcers three times daily for up to 14 days. Daily discomfort was reduced by half (P less than 0.01) and less pain (P less than 0.05) was experienced by the treated group. Treatment with 5-ASA shortened healing time (7 vs. 11 days, P less than 0.01) and reduced the difficulty in eating (P less than 0.05). No significant side-effects were reported. We believe 5-ASA cream to be an effective treatment for aphthous ulcers.