In the present investigation the frequency of oral ulcers and pain in 79 adults orthodontic patients was recorded. Only four of all patients had never had oral ulceration during treatment, but 83% of the patients characterized the trouble as minor. About 47% of the patients said that ulcers caused by the fixed appliance were the most annoying part of the treatment, and 38% said that activation of the appliance caused the most discomfort. In about 63% of the patients there was less pain when the treatment had lasted for some months, and in 24% there was no significant change in the discomfort. The pain following activation lasted for only 2-3 days (71%), but 20% had pain for more than 3 days, and five individuals felt pain constantly. The recurrence of aphthous ulceration (RAU) was not significantly affected during the orthodontic treatment, and in only one case was there an increase in the occurrence of herpes labialis.