RESUMEN
Congenital dilatation of the submandibular duct also known as imperforate submandibular duct is a rare condition of unknown etiology, clinically characterized as a well-defined, fluctuant swelling in the floor of the mouth, and microscopically defined as a cystic cavity covered with pseudostratified columnar epithelium consistent with a dilated salivary duct. A 1-month-old female presented with a translucent, smooth cystic swelling in the floor of the mouth causing breastfeeding difficulty. The lesion was surgically excised and microscopically, a cystic cavity lined with pseudostratified columnar epithelium was observed. The final diagnosis was congenital dilatation of the submandibular duct. Dentists and otolaryngologists should consider congenital dilatation of the submandibular duct when evaluating fluctuant swelling in the floor of the month of infants.