The investigation was undertaken to find out whether favourable conditions for healing after periodontal surgery would develop in patients whose oral hygiene was professionally maintained at a high standard. The study was performed on 20 patients with advanced periodontal disease. Following an initial examination, comprising plaque index and gingival index scoring, measurement of pocket depths and loss of attachment, the patients were randomly distributed between a test and a control group. The patients first received professional cleaning of the teeth once every 2 weeks. The patients of the control group were recalled for scaling of the teeth once every 6 months. All patients were reexamined after 6, 12 and 24 months. It was found that the control patients were unable to maintain a high standard of oral hygiene with the result that the treatment of the periodontal disease failed. The patients of the test group maintained a high standard of oral hygiene, and the treatment of the periodontal disease was, therefore, successful.