Objective: Klippel-Trenaunay syndrome (KTS) is characterized by triad of venous varicosity, naevus flammeus, and soft/hard tissue hypertrophy. Manifestations of the syndrome in the head and neck region are rare, but in some cases hemangioma of the lips, tongue, and gums, open bite and cross bite, and early tooth eruption are associated with the disease. Study design: We report a 12-year-old KTS patient with gingival hyperplasia, congenital missing teeth, and increased mucosal vascularization as oral manifestations. Results and conclusion: All manifestations of the KTS were observed on the same side of the head, except bilateral missing teeth. Histological examination showed several vascular enlargements in enlarged gingiva. It is suggested that oral manifestations of the syndrome are generally related to the severity of the disease, but they do not always present in the same pattern.