Diogenes syndrome is characterized by shameless neglect of the body and personal environment, hoarding, and the rejection of any help. It occurs among patients with and without other psychiatric disorders. The initial treatment should be a behavioral program, but there is no information about the pharmacological treatment of this syndrome. We report the case of a 77-year-old woman with symptoms of Diogenes syndrome. After an unsuccessful behavioral program, treatment with risperidone initially improved the behavioral symptoms but impaired cognitive function, and was followed by marked global deterioration, fulfilling criteria for dementia.