In general dental conditions such as dental caries and periodontal disease, a combination of adverse conditions can cause potentially life-threatening periodontal abscess. We treated a patient in whom an oral infection developed into septic shock, resulting in patient death. A 78-year-old woman experienced spontaneous pain around a moving tooth. Pus discharge was observed, the area was sterilized, and an analgesic was prescribed. A few days later, the swelling spread to the buccal region leading to difficulty while eating. Upon systemic status and blood examination at our dental hospital, depressed consciousness due to dehydration and septic shock were suspected. Oxygenation and infusion of acetate linger with antibiotics were immediately performed. Furthermore, a blood examination revealed malnutrition and a severe infection; therefore, the patient was transferred to a nearby general hospital. However, the patient died the next day because of advanced disseminated intravascular coagulation and multiple organ failure. When an oral infection is suspected in an elderly patient, antibiotics should be quickly administered, the patient's local and systemic state should be confirmed, and sterilization should be performed daily. If no improvement is observed, medical attention should be quickly sought.