We report a case involving a 12-year follow-up after treatment for chronic periodontitis with furcation involvement. A 54-year-old woman presented with the chief complaint of hypersensitivity. Clinical examination at the first visit revealed 15% of sites with a probing depth ≥4 mm and 35% of sites with bleeding on probing. Initial periodontal therapy was implemented based on a clinical diagnosis of severe chronic periodontitis. Surgical periodontal therapy was subsequently performed at selected sites. For #44, regenerative periodontal therapy using enamel matrix derivative (Emdogain(®)) was selected. For #16, which exhibited a 2- to 3-wall vertical bony defect and class III (mesio-distal) furcation involvement, bone graft was scheduled. Other sites with residual periodontal pockets were treated by open flap debridement. For #37, with a gutter-shaped root, odontoplasty was performed. After reevaluation, the patient was placed on supportive periodontal therapy (SPT). During 12 years of SPT, the periodontal condition remained uneventful in most of the teeth. However, bone resorption was observed in the distal aspect of #37, making the prognosis poor. This indicates the need to continuously monitor risk factors, including inflammation and traumatic occlusion, during SPT. Although some problems still remain, severe periodontitis with furcation involvement was successfully maintained longitudinally with an adequate level of patient compliance and careful SPT.