:We report a case of bone resorption inhibitor-related osteonecrosis of the jaw (ARONJ) in an 85-year-old woman with dementia and breast cancer. Although we initially selected conservative therapy, we switched to surgical therapy due to the progress of osteonecrosis. Prior to extensive sequestrectomy (sequestrectomy and surrounding bone shaving) under general anesthesia, it was necessary to solve various problems such as breast cancer control, underlying disease problems, and family cooperation. The postoperative course was favorable and no recurrence was noted until 15 months. It is expected that the number of elderly ARONJ patients with cancer and dementia will increase in the future.Therefore, oral surgeons should be able to collaborate with multiple occupations flexibly and appropriately.