Purpose: Whereas oral ranula is relatively common and presents as a cyst in the mouth, the plunging ranula is rare and manifests itself as a mass in the neck with or without an associated oral lesion. The purpose of this study is to examine the clinical characteristics of rare bilateral plunging ranula arising from accessory submandibular gland in order to provide our experience for its correct diagnosis and treatment. Methods: A 13-year-old girl manifests as a slow growing painless, non-mobile swelling in the anterior neck. She underwent surgery via a cervical approach. A pseudocyst was extirpated and adjacent accessory gland tissue and related lymph node were removed. Results: The histologic appearance is characteristically of a cyst, devoiding of epithelium or endothelium, with a vascular fibro-connective tissue wall containing some chronic inflammatory cells and macrophage stuffed with mucin. Pathologic findings represented a form of myxomatous degeneration and lined by condensed connective tissue and granulation tissue. The nature of the accessory gland tissue was same as subligual gland. Although total submandibular or sublingual gland excision was not performed, no recurrence was observed during 6 months follow-up periods. Conclusion: Usually, unilateral plunging ranula develops commonly because of rupture of sublingual gland duct by trauma and extravasation of salivary secretion to the adjacent tissue. But our case developed because of bilateral congenital accessory submandibular gland. This is thought to be a result from a congenital failure of canalization of the terminal end of the duct. Finally, the correct diagnosis is essential for the most effective treatment, which is excision of the ranula and related accessory salivary gland. We performed excision of accessory submandibular gland and plunging ranula and had a good result without recurrence.