Cross-sectional and longitudinal studies have identified that persons wearing overdentures require regular care and maintenance of the remaining dentition. This paper reports on a longitudinal study of the periodontal problems of 254 patients seen over a period of 12 years. At overdenture placement, baseline measurements and photographs were made by a single examiner. These measurements included evaluation of the restorations; abutment height above the gingival margin measured at midmesial, middistal, midfacial, and midbuccal; and periodontal probing depths measured at the same four sites. Oral hygiene and denture status were also evaluated. Patients were asked to return at 6-month intervals for evaluation using similar indices. Plaque and calculus were a common finding, especially in the mandibular arch. Serious periodontal problems were not common; however, it was clear that a high-risk group existed in this population. Bleeding on probing proved to be the most reliable clinical predictor of periodontal problems.