This article constitutes the first of a series directed to review fundamental disorders in clinical psychogeriatrics. This sort of publication is intended to retrieve clinical practice as the cornerstone for research and teaching in psychiatry. Besides, and particularly in geriatry, we try to expand the strategy of liaison work with primary physicians. In this case, a nosological review of the so called "delusion of negations" is presented. The Jules Cotard's original concept of subtype of delusional melancholia is contrasted to the view of numerous authors in this century who have described it as a form of non-specific delusional syndrome.