PURPOSE: Congenital midline upper lip sinus is a rare lesion. There are two postulates that can account for the formation of the upper lip sinus based on two major theories of the development of the face: the fusion theory and the merging theory. However, congenital midline lower lip sinus is very rarely reported and described. We report a case of a congenital midline sinus of the lower lip in a 6-year-old female. METHODS: A 6-year-old girl presented with a nipple like swelling on the midline lower lip. Physical examination revealed about 5x5mm protruding round mass with a just small opening that was non-tender to palpation. The mass was not associated with any skin changes. It umbilicated at the apex and contains a fistulous tract, discharging clear fluid. Only, simple radiologic finding shows bony spur on the lower one third of mandibular symphsis. RESULTS: A small transverse ellipse is made around the opening and elevated mass with sharpe dissection. The tract is excised using the probe and dye as the guide. The tract was extended to periosteum of the lower one third of the mandible. The tract and involved periosteum were excised en bloc, and removed protrusion of the mandibular bone using diamond burr. Microscopic examination of the resected sinus revealed the fistulous tract itself, consisting of fibrous connective tissue covered with cornified stratified squamous epithelium, was observed in the center of the sample. In 6 months follow-up, This patient had a good result was obtained by the method of fistulectomy alone. CONCLUSION: Midline cranoifacial fistulas represent rare lesions resulting from abnormal fusion of embryologic structures. Our case report describes the excision of a congenital midline sinus of the lower lip in a 6-year-old female. This case represents the first report of a lower lip sinus presenting in a girl as a mass in the skin of the chin with extension to the midline of the mandible. However, the etiology of this rare congenital sinus remains obscure.