The aim of this article is to suggest that hostile behavior in elderly patients is often caused by a reversible mood disorder rather than by a personality disorder or dementia, even if these two last diagnoses are already well established. Sedatives, often prescibed for hostile behavior, can induce confusion, falls, and bedridden states, and can actually increase the rate of mortality. The mood disorder can be a hostile agitated depression or a mixed affective state. The hypothesis of a mood disorder calls for an antidepressant trial, possibly combined with a mood stabilizer.