Simple schizophrenia: past, present, and future.

The diagnostic category called simple schizophrenia has disappeared from official American nosology but has been retained in ICD-9. The diagnosis has a long history, was one of the traditional schizophrenic subtypes identified by Bleuler, and was later accepted by Kraepelin. The authors provide a historical overview of the concept, review its modern successors, and provide recommendations for its inclusion in DSM-IV as a proposed diagnostic category needing further study.