Aphthous ulcers were found in 2% of a total of 20,333 individuals aged 15 years or more examined in urban, suburban, and rural regions of Sweden. When a history of 2 years was considered, the prevalence was 17.7%. A slight predominance was found for females. The younger age groups showed the highest prevalences of the condition, which then decreased steadily with age. Interviews were conducted with a fraction of the population comprising 2771 people with regard to their experiences of aphthous ulcers. Thus, for example, the average number of episodes per year was two to four and the most prevalent time for healing, 5-8 days. Among the factors thought by patients to trigger the condition, catching a cold was reported as the main one, followed by stomach problems and menstruation.