A number of investigations have now shown that the rates of mental disorder among inmates in correctional facilities in North America far exceed the rates for these disorders in the general population (Collins & Schlenger, 1983; Daniel, Robins, Reid, & Wilfey, 1988; Hodgins & Ce Hyde & Seiter, 1987; Motiuk & Porporino, 1991; Neighbors et al., 1987; Teplin, 1990a). The rates of major disorders (schizophrenia and major affective disorders) have been found to be up to four times greater than the genera1 population rates matched for sex. These recent studies have further suggested that, in a large majority of cases, the major disorder had been present before the current period of incarceration. Previous estimates of the prevalence of mental disorders among offenders had suggested that only about 5% of inmates suffered from psychosis. However, these estimates were obtained using various diagnostic criteria, reliabilities of the diagnoses were not examined and/or reported, samples were small and biased (usually those referred for treatment), and comparable prevalence rates for the general population were not available (for a review of these older investigations, see, for example, Roth, 1986; Wormith & Borzecki, 1985). The new studies succeeded in correcting many of the methodological weaknesses that characterized the older investigations. They examined representative samples of inmates, all used the DSM-III criteria, and all but one (Hyde & Seiter, 1987) used the same standardized, reliable, and valid diagnostic tool that had been used to obtain prevalence rates of mental disorder in the genera1 population (the Diagnostic Interview Schedule, DIS, Robins, Helzer, Croughan, & Ratcliff, 1981). Interviewers were specifically trained to use the instrument and supervised during the course of the study to ensure that they adhered to the rules of the instrument, and these studies examined and reported inter-rater reliabilities for the diagnoses.