All penetrating neck wounds are potentially dangerous and require emergency treatment, because there are important vessels, nerves, and organs in the neck. We report the rare case of a 71-year-old man with neck injury caused by a glass fragment that penetrated into the floor of the mouth from the submandibular region. The patient had accidentally fallen through a glass door and sustained a 15-cm long incised wound in his neck. He was initially transferred to a district hospital, where he was diagnosed as having arterial bleeding and a neck injury penetrating into the oral cavity; ENT surgeons at the hospital performed temporary hemostasis and tracheotomy under local anesthesia, and the patient was urgently transported to our hospital by ambulance. On admission, he was conscious, and his general condition was good. CT showed no damage to the major vessels, but revealed free air around the sublingual region. Therefore, emergency surgery was performed to repair the perforation from the neck into the oral cavity under general anesthesia. We found the facial artery and facial vein and ligated them during the operation, and the opening into the oral cavity was closed with absorbable sutures. The postoperative course was good, the patient resumed oral intake on day 4 after the surgery, and he was discharged from the hospital on day 9 after the surgery, with the only postoperative complication of palsy of the marginal mandibular branch of the facial nerve. In this report, we review nine cases of neck injury penetrating into the floor of the mouth and 11 cases of neck injury caused by a glass fragment reported in the literature and discuss their clinical findings.