Schizophrenia is a psychiatric illness that can be profoundly disabling and is usually chronic in nature. The cause is not known, but there appears to be a genetic predisposition. The etiology has been conceptualized in a stress/diathesis (vulnerability) model: Biological and environmental factors (e.g., drug abuse, psychosocial stresses) interact with a genetic vulnerability to precipitate the illness. Several theories have been proposed to explain the observed biological abnormalities of the disorder, including over-activity of the dopamine neurotransmitter systems in the central nervous system, changes in brain structure (e.g., enlargement of the lateral cerebral ventricles) and brain function (e.g., decreased frontal lobe function [hypofrontality], as evidenced by diminished blood flow, and deficits in attention and sensory filtering). Psychological and social factors are considered important in the expression and course of the disorder. It is likely that schizophrenia constitutes a group of disorders rather than a...