The study is a complication of data on oral mucosal lesions collected among 20 333 people aged 15 yr and over. The aim was to calculate the correlation between the prevalence of recurrent aphthous ulcers and various tobacco habits. The prevalence of aphthous ulcers in the population was 17.7% including cases referring to episodes within the last 2 yr. There was a negative correlation between the prevalence of ulcers and tobacco habits. The suppression of ulcers was most evident for those groups smoking pipe or cigarettes without filter and only moderate for those using snuff. Further, heavy smokers had a lower frequency of ulcers than moderate smokers.