Plunging ranulas most commonly occupy the submandibular triangle and misdiagnosis inevitably leads to incorrect treatment. Three cases of plunging ranula are reported. The correct diagnosis resulted from the characteristic signs of magnetic resonance imaging (MRI). Treatment consisted of the total removal of the sublingual gland and evacuation of cystic contents by the intraoral approach. The cyst gradually regressed and disappeared within two months after surgery as confirmed by ultrasonography. All three cases have not experienced recurrence in the follow-up period. MRI is a valuable method to correctly diagnosis plunging ranula. Total removal of the sublingual gland is the most reliable method to treat plunging ranula.