Purpose: Previous studies have indicated that health beliefs are related to the periodontal disease status and treatment behaviour of patients. However, it is possible that treatment may affect a patient's health beliefs and thus complicate this issue. The present study therefore looked for changes in health control beliefs and oral health impacts in patients undergoing periodontal treatment in a dental school. Materials and Methods: Questionnaires assessing dental multidimensional locus of control (LOC) and oral health impact profile (OHIP) were posted to subjects due to attend for initial periodontal consultation and were returned by 127 patients who attended. Repeat questionnaires were sent to all subjects 6 months later when they had received some oral hygiene instruction, scaling and root planing, and 55 were returned. Results: Comparison of data for those subjects who completed both questionnaires showed no difference in LOC but showed a trend (p = 0.065) towards reduced OHIP (i.e. improved oral health-related quality of life). Conclusions: These subjects apparently did not alter their health control beliefs about periodontal disease as a result of treatment, but there may have been an improvement in their oral health-related quality of life. Further studies are required to confirm these possibilities. Schlagwörter: locus of control, oral health impact profile, periodontal treatment, quality of life