Osteoradionecrosis (ORN) is one of the common late adverse effects that follow radiation therapy for head and neck cancers. ORN usually develops on the mandible and less frequently on the maxilla. We present three cases of ORN of the cervical vertebrae, which is rarely reported. Two patients suffered from secondary osteomyelitis after neoadjuvant chemotherapy followed by definitive concurrent chemoradiation therapy with a hyperfractionated and an accelerated hyperfractionated regimen, respectively. For these patients, the high intensity of treatment was considered the cause of ORN. The third patient underwent concurrent chemoradiation therapy for upper thoracic esophageal cancer and subsequently underwent endoscopic laser resection and radiation therapy for hypopharyngeal cancer. ORN developed in the area of reirradiation. In this case, an excessive radiation dose was considered the cause. ORN of cervical vertebrae, different from that of the mandible and maxilla, has a risk of radiculopathy and myelopathy. In the future, ORN of cervical vertebrae will increase because metachronous double cancers will increase and opportunities for reirradiation, in turn, will increase. To prevent this, it is necessary to optimize the treatment schedule for radiation therapy, including the total dose, fractionation, and concurrent chemotherapy, and to decrease the volume of cervical vertebrae within the irradiation field.