A 77-year-old man with a history of diabetes was diagnosed with herpes zoster (HZ) involving the mandibular nerve. He was hospitalized in the dermatology department and acyclovir (ACV) administration was initiated. Abnormal behavior observed on the following day raised suspicion of ACV encephalopathy, and the ACV was discontinued. As pain control was insufficient, the patient was referred to the pain clinic. Treatment relieved the pain, and the patient was discharged. On day 51 after onset, he complained of lower-left tooth loss and was referred to our oral surgery department. With the diagnosis of lower-left jaw osteonecrosis, sequestrectomy was performed under general anesthesia. Cases of HZ occurring in a trigeminal nerve branch II and III distribution, with successive loss of teeth and jaw osteonecrosis, have been reported. Physicians should be aware that HZ can be associated with this complication. In the present case, insufficient administration of antiviral drugs for HZ may have been a factor.