Hereditary gingival fibromatosis (HGF) is a rare condition affecting the gingiva and may or may not be a clinical feature of other syndromes. It has been classified as a nondental biofilm-induced gingival disease. The pathogenesis of this condition has been poorly understood till date. Although different genetic mutations have been implicated to play a role, there is considerable interest on an addition mutation of Son of Sevenless-1 (SOS-1) gene. We report a case of a 27-year-old male patient who came to us with the complaint of enlarged gums of several years\' duration. There were other members in his family who were similarly affected. After the clinical diagnosis of HGF was confirmed, the patient and his available family members were subjected to a genetic analysis for identification of mutation in SOS-1 gene, which turned out to be negative. The patient was treated with nonsurgical periodontal therapy and is under regular follow-up. To the best of our knowledge, this is the first study to assess SOS-1 mutation in an Indian family.