We report the case of a 69 year-old female patient who was hospitalized for Diogenes syndrome, defined by marked self-neglect, social withdrawal and excessive hoarding, leading to squalor. Somatic causes were eliminated. Her personal history showed an eight-year depressive episode followed by a 20-year hypomanic episode without remission, followed by a persistent manic episode associated with Diogenes syndrome for four years. The Diogenes syndrome was successfully treated with mood stabilizers. Mood disorders - in particular chronic mania (i.e. a manic episode lasting more than two years) - should be considered in cases of Diogenes syndrome and in current classifications.