A case of ranula in a neonate is reported. A 2-month-old infant was found to have a small swelling in the floor of the mouth at birth. Initial examination revealed a fluctuant, translucent swelling with protrusion from the mouth. The lesion arose in the left side of the mouth floor. A computed tomographic examination confirmed the presence of a cystic lesion, un associated with the sublingual gland. The clinical diagnosis was a sublingual ranula. Although marsupialization was performed three times, the swelling recurred and returned to its original size soon after treatment. Three months later, extirpation of the cyst and the sublingual gland was performed. The postoperative course was uncomplicated, with no signs of recurrence for 6 months. The histological diagnosis was mucous retension cyst. To prevent recurrence, extirpation of the sublingual gland was effective, even in an infant.