The major mental illnesses, most notably schizophrenia and other psychotic disorders, typically have their onset in young adulthood, and often lead to a lifetime of chronic disability. The possibility of preventing these illnesses has received increasing attention in the past few years (McGorry & Edwards, 1998; Wyatt, Apud, & Potkin 1996). This trend has been fueled by evidence that the longer the duration of the initial untreated episodes of psychosis, the worse the long-term prognosis (Wyatt, 1995). Also, the availability of atypical antipsychotic medications that have fewer immediate side effects has contributed to interest in psychosis prevention.

The first step in the prevention process is the identification of vulnerable individuals. It is well established that the clinical onset of schizophrenia is preceded by behavioral dysfunction. In some cases, preschizophrenic individuals manifest consistent dysfunction that is apparent within the first few years of life, extends throughout childhood, and becomes more pronounced in adolescence (Larsen, McGlashan, Johannessen, & Vibe-Hansen, 1996; Walker, Baum, & Diforio, 1998). Others show relatively normal childhood development, then a precipitous decline that begins in adolescence. Based on the best available evidence, about 70 percent of adult-onset patients manifested behavioral dysfunction in adolescence (Larsen et al., 1996; Neumann, Grimes, Walker, & Baum, 1995; Yung & McGorry, 1996). Thus, many view adolescence/early adulthood as the most plausible developmental stage for initiating prevention.

In parallel with the increasing emphasis on prevention, there has been a resurgence of interest in the neurodevelopmental changes that accompany pubertal maturation.