As in all medical disciplines, diagnosis in clinical psychiatry should be reached in a step-wise approach: after assessing the chief complaint of the patient, a careful examination of the psychopathology follows e.g. by using the AMDP system [1] to preliminarily conclude the process with a syndromal classification [2]. This syndromal classification is of great importance as it guides the initiation of therapy in daily life practice. After gaining additional information (e.g. investigation in the course of the disease, brain imaging, thorough assessment of cognitive function, exclusion of organic causes) a final diagnosis is possible. Unfortunately, a premature jumping to diagnosis is not uncommon (with the potential consequence of incorrect therapies).

In addition to these difficulties, recent neurobiological research has shown that nosologic assignments through conventional diagnostic classifications are far less specific than assumed, revealing a large overlap between diagnostic categories [3,4], e.g. between Schizophrenia and affective disorders. Consequences of this finding are discussed both for the construction of future classification systems and for therapy.