Cowden syndrome, also known as multiple hamartoma syndrome, is a rare autosomal dominant disorder characterized by multiple hamartomas and a high risk of development of malignancy. Oral findings, such as papillomatous lesions and fibromas, are common features; however, a periodontal phenotype has not been reported previously. Therefore, this report presents a case of gingival overgrowth associated with Cowden syndrome, its successful surgical management, and the 12-month follow-up results. Additionally, we discuss the implications for clinicians. A 23-year-old woman was referred to the Department of Periodontics, Piracicaba Dental School, presenting with generalized gingival overgrowth. A detailed dental and medical history and clinical examination confirmed the systemic diagnosis of Cowden syndrome. Histology, radiographs, and clinical data document the entire clinical approach and follow-up. Clinically, there were minor signs of recurrence of gingival overgrowth in a 12-month period after gingivectomy; however, papular lesions reappeared in keratinized gingiva immediately after healing. No signs of bone loss related to the systemic condition were observed radiographically. Histologically, a dense connective tissue with a moderate chronic inflammatory infiltrate and epithelial acanthosis, which is characteristic of gingival hyperplasia, were demonstrated. Gingival overgrowth may occur as an oral phenotype related to Cowden syndrome and can be successfully treated by means of external bevel gingivectomy, followed by regular maintenance therapy, contributing to the patient's well-being, both functionally and esthetically. Keywords: Cowden syndrome, gingival hyperplasia, gingival overgrowth, gingivectomy, multiple hamartoma syndrome, oral manifestations