Criminality is common among patients with severe mental disorders and/or substance use disorders (SUDs).

To study the incidence of imprisonment among psychiatric inpatients along with their diagnoses patterns and survival.

This is a nationwide register based study of all psychiatric inpatients admitted in Iceland between 1983 and 2007. The database contained information on discharge diagnoses, imprisonment and cause of death when relevant. Cumulative incidence of imprisonment was calculated using the Kaplan-Meier method. Using a nested case-control (1:3) design, survival was analysed with Cox-proportional hazard ratio model. Controls were similar regarding age, year of admission and discharge diagnoses. All analyses were done separately for men and women.

Men admitted at ages between 18 and 30 had 21% cumulative incidence of incarceration over a 20-year period. For women the corresponding figure was 6%. Most common discharge diagnoses of those serving a sentence in prison were SUD and/or personality disorder. Among men, adjusted hazard ratio (HR) for risk of death was 2.0 (95%-confidence interval (CI): 1.5–2.6) and for women 1.3 (95%-CI: 0.5–3.5).

Imprisonment is common among psychiatric inpatients. This group represents individuals with long-term problems and specific treatment needs. Mortality was significantly increased for men while there were to few women in the cohort to establish meaningful HR for risk of death.