The relationship between crime and mental illness is poorly known and managed. Criminals very frequently receive insufficient treatment for their mental illnesses, due to a lack of secure hospital space and refusal to accept treatment, among other things.
Important factors, frequently transcending all countries, associated with a high prevalence of mental disorder in prisons are: (1) The criminalization of mentally ill individuals by pressing charges instead of tolerating socially deviant behaviour; (2) Economizing on the treatment of mentally disordered individuals by reducing the services of psychiatric institutions (keyword deinstitutionalization) and complementary community-based care structures, especially for young adult chronic psychiatric patients; (3) Strict criteria for civil legal or public legal confinement, which appear to be best met by the penal system for individuals with abnormal and legally deviant behaviour who require therapy but are unwilling to comply; (4) The reluctance of general psychiatric facilities to accept mentally disordered prisoners; (5) The rejection of 'difficult' chronic psychosis patients because of doubts about their suitability for treatment; (6) A political climate that keeps the resources for mentally disordered offenders at a low level.
In 1990, the UK Home Office reported that more than a fifth of sentenced prisoners in the UK (about 7,000) were mentally ill, including many in acute need of psychiatric treatment they do not receive. 35% of women prisoners and above 20% of young men fell into this category. The conclusions were based on interviews with over 2,000 prisoners -- 5% of the sentenced prison population. The number of acute cases was at least 10 times higher than previous official figures. 3% were diagnosed as so ill that they should certainly be moved to a hospital. Nationally this implies more than 1,000 severely mentally ill prisoners, with probably the same number for those on remand. Nearly 40% of the 48 people who killed themselves in 1989 had a history of mental illness before they were imprisoned. In the USA, an average 15% of people in prison were considered mentally ill. Many had found their way into prisons after mental hospitals were closed.