Introduction: Gingival fibromatosis (GF) is a condition characterized by progressive enlargement of the gingiva caused by an increase in the size of submucosal collagenous connective tissue. GFs can be either hereditary or idiopathic. Idiopathic gingival fibromatosis (IGF) is a rare, benign, asymptomatic, nonhemorrhagic and nonexudative proliferative fibrous lesion of the gingival tissue.

Case Presentation:A 30-year-old female patient was referred to the department of oral and maxillofacial surgery with a painless swelling in the lingual region of the right mandible. It was determined that there was no systemic disease and pregnancy present in her medical history, also she did not use any medication. The patient stated that the swelling had been growing slowly since 2021. Intraoral examination revealed a tight, pink colored, non-bleeding pedicled soft tissue in the mandibular lingual region, extending from the midline to the posterior of the ramus, at the occlusal level of the teeth. The lesion was removed by excisional biopsy under local anesthesia and sent for histopathological examination. On histopathological examination the lesion was diagnosed as fibromatosis. No recurrence was observed at ten months follow-up.

Conslusıon: Patients with idiopathic gingival fibromatosis lack a family history of gingival hyperplasia and have no identifiable causative factors (pregnancy, medications, systemic conditions, etc). After carefully ruling out all known causes of the gingival enlargement, a diagnosis of IGF may be rendered. Recurrence in patients with GF is unpredictable but is most often seen in children and teenagers, rather than adults. Keywords: Excision, fibromatosis, idiopathic, mandible