A localized periodontal defect associated with an unusual furcation on a mandibular central incisor and its treatment sequences are presented. A 54-year-old woman presented with a persistent localized periodontal defect, which was not responsive to nonsurgical periodontal therapy. An exploratory surgery revealed complete through and through furcation involvement on the right mandibular central incisor, resulting in a three-walled infrabony defect. Following thorough mechanical debridement and root planing, the infrabony aspect of the defect was grafted with freeze-dried bone allograft combined with the recombinant human platelet-derived growth factor-BB. The flaps were positioned to enable patient's home care and professional dental cleaning. Follow-up examination revealed uneventful healing and resolution of the infrabony periodontal defect. Clinicians should be aware of this unusual condition and consider it as a potential etiology when dealing with a persistent localized periodontal defect in the mandibular anterior sextant, which may not respond to the conventional nonsurgical periodontal therapy. Eliminating the active disease as well as enabling careful maintenance and oral hygiene may prevent further deterioration and result in a stable long-term outcome preserving the compromised tooth. Keywords: furcation, guided tissue regeneration, infrabony defect, recombinant human platelet-derived growth factor-BB, tooth anatomy