Recently, the validity of the simple dichotomy between positive and negative symptoms in psychosis has been questioned. A newly admitted group of 114 DSM-III patients with psychotic disorder were assessed using Andreason's positive and negative symptoms scales. Multidimensional scaling, augmented by cluster analysis, was applied to the full item set of these scales and showed clearly that there are three major, independent groups of symptoms: Hallucinations/Delusions, Positive Thought Disorder and Negative Symptoms. Within the Hallucinations/Delusions and Negative Symptoms groups there was some additional structure which does not conform to the SAPS and SANS sub-scales. In particular there was considerable heterogeneity within the Hallucinations/Delusions group, and delusions of persecution may represent a fourth independent dimension of psychopathology which is under-represented in these scales.