The history of nosologic approaches to paranoid schizophrenia and the other paranoid psychoses is traced from the time of Kraepelin. Kraepelin, emphasizing the course of illness, proposed a narrow definition for paranoid dementia praecox (paranoid schizophrenia). He created the entity of paraphrenia for cases with symptoms similar to those in paranoid dementia praecox but without a deteriorating course. Bleuler, emphasizing underlying psychological mechanisms, broadened the concept of paranoid schizophrenia to include nearly all delusional functional psychotic states. After Bleuler, the controversy continued as to whether the paranoid psychoses belonged within or separate from the schizophrenic disorders. Emerging from these historical controversies, current nosologic approaches to paranoid schizophrenia and paranoid psychosis differ substantially. Approaches to paranoid schizophrenia range from broad global criteria, which include patients with thought disorder and affective deterioration (e.g., ICD-9), to narrow criteria such as those proposed by Tsuang and Winokur (1974), which specifically exclude such patients. While some criteria for paranoid psychosis exclude patients with hallucinations or other than persecutory or jealous delusions (e.g., DSM-III), other criteria include such patients.