Biological findings such as low 5-HIAA levels in cerebrospinal fluid (CSF) in suicidal patients compared to non-suicidal patients independent of the type of psychiatric disorder indicate a broad basis for suicidality. It is therefore important to ask whether a suicidality syndrome can be delineated on a phenomenological level, and whether it is independent of specific major psychiatric disorders which are otherwise considered to be aetiologically different. This paper reports on a study of 2383 schizophrenic and 1920 depressive unselected patients with and without suicidality. They were assessed during the first 24 h after admission to a psychiatric in-patient facility using a comprehensive psychopathological assessment (AMDP system). Using multiple variance analysis and logistic regression analysis based on single symptoms, for both suicidal and non-suicidal patients it was shown that a suicidality syndrome independent of the underlying illness can be delineated. In schizophrenia as well as in major affective disorders it was found that hopelessness, ruminative thinking, social withdrawal and lack of activity are core symptoms of this suicidal syndrome. The finding of a suicidality syndrome, not associated with a specific major affective disorder, indicates the need to identify this syndrome, which should be seen as an independent dimension and diagnosed separately, and not regarded merely as a secondary symptom of major psychiatric disorders, particularly affective disorders.