Abstract: This study was conducted to determine the prevalence of oral aphthosis in a normal population in Iran, using the data of the WHO-ILAR COPCORD study in Iran. We conducted this study in Tehran, the capital of Iran which was selected as the COPCORD study field. In 22 districts of Tehran, 50 clusters were randomly selected. Of the selected houses, 4,096 households were visited and 10,291 persons were interviewed (response rate of 75%). Out of the 10291 subjects interviewed, 2592 had aphthous ulcers which translated to a prevalence of 25.2% (95% confidence interval: 24.4% to 26.0%). The prevalence of oral aphthosis was rather high in this normal population. Archives of Iranian Medicine, Volume 11, Number 2, 2008: 207 – 209. Keywords: Behçet’s disease ● Iran ● oral aphthosis