The vocabulary used in a scientific field undergoes continual change and refinement. Especially in a dynamic, clinical science such as psychiatry, definitions are modified to take into account new information about illness and recent developments in research. As more becomes known, the use of language becomes more precise as does the application of diagnostic criteria. This glossary incorporates the revised nomenclature of the American Psychiatric Association's new Diagnostic and Statistical Manual (DSM III). Diagnostic terms have been arranged and cross-referenced to allow easy use of the glossary by those familiar with the older nomenclature.