Evidence from several studies supports the neurodevelopmental hypothesis of schizophrenia. Others suggest a substantial body of evidence attesting to a possible neurodevelopmental origin of affective disorders. However, there is little evidence that any risk factor or neurodevelopmental marker is specific to any diagnostic category within functional psychoses. Some authors have proposed a new model which implies a continuity within the category of psychosis based on a psychopathological continuum. This research strategy has important and useful advantages which are discussed in this review.