Diogenes was a Greek philosopher who was also known as Diogenes the Cynic. In 1975, Clark identified a condition called Diogenes syndrome, which is a neurobehavioral syndrome found among elderly people who, due to self-neglect, show unhygienic appearance, live in dirty and messy set-ups, and are not ashamed of these. In this study, we examine a case of Diogenes syndrome caused by behavioral variant frontotemporal dementia (bvFTD). A 56-year-old man showed behavioral disinhibition since year X-3 along with apathy, loss of sympathy and empathy, compulsive behavior, and dietary changes since year X-1. He was admitted to our hospital in year X. He was in the habit of over-spending; for example, he bought two automobiles and was in a debt of several million yen. Electricity and gas services to his home had been stopped, and he had not bathed for six months. The floor of his house was covered with garbage, including about 300 bottles of energy drinks and other food items. He was subjected to a neuropsychological test, which revealed frontal dysfunction. MRI showed frontal atrophy and SPECT showed frontal hypoperfusion. The eventual diagnosis was that of Diogenes syndrome due to bvFTD, and we adjusted his environment for admission into a facility. A case report of Diogenes syndrome caused by bvFTD has never been made in Japan. In this case, as the syndrome developed after his divorce, it is possible that the presence of a spouse prevented the onset of the disease. In addition, patients with Diogenes syndrome tend to reject aid, which makes intervention difficult. However, he was receptive to the intervention and did not resist the disposal of objects. The course of this case and previous studies suggest that interventions for Diogenes syndrome with bvFTD are effective. Early intervention in Diogenes syndrome is important because it may cause not only deterioration of life prognosis but also hygienic and financial damage to the neighbors. Many municipalities are having trouble dealing with homes that are similarly dirty and neglected. We propose that cooperation between local governments and medical institutions is necessary to realize the accumulation of cases, early detection, and early intervention. We obtained consent for case reporting and have taken care to protect privacy.