Aim: To evaluate why some patients with advanced periodontal disease following initial periodontal and orthodontic treatment, when followed long-term, may continue to show bone loss. Method: Two cases, followed 21 and 25 years, are described. Results: The first patient's periodontium deteriorated because of failure to continue her periodontal maintenance program long-term. The periodontium of the second patient deteriorated despite excellence in home care and periodontal recall visits. She was considered refractory to treatment. In both cases, however, orthodontic treatment was considered helpful because it created favorable esthetic and functional alignment of teeth and allowed critical prosthetic reconstructions. Conclusion: Although bone loss occurred, orthodontic treatment was beneficial and contributed to the interdisciplinary treatment of these patients. World J Orthod 2001;2:244–252.