Reclassifying psychotic disorders in the upcoming revisions of the mental disorders section of ICD-10 and DSM-IV will first necessitate the development of a unified and operationalized definition of the term "psychosis". Ideally, such a definition would be harmonized between both groups of diagnostic classification systems and become part of a glossary of terms. Conceptually and based on epidemiological and some genetic work, incorporating dimensional criteria and criteria for prodromal high-risk symptoms may become feasible. Considering the currently available evidence from genetic, neuroimaging and neurophysiological studies, none seems yet sufficiently validated to warrant major changes. However, further research in these areas promises to yield important new insights which may become relevant for the classification of psychotic disorders in the near future. Given the rapid progress in these fields, regular updates of the classification criteria at shorter intervals than in the past may become necessary.