Data were obtained from the Stockholm County In-Patient Register on 1,056 patients (546 men and 510 women). The median age of these patients was 42 years, and the age range was 17-70 years. All patients were followed up 10 years later in the Police Register and 7 years later in the Cause of Death Register. It was found that mental patients were overrepresented in criminality statistics. Of those who were 40 years of age or younger at the time of discharge, nearly 40 percent had a criminal record, as compared to less than 10 percent of the general public. The most frequently occurring crimes were violent crimes, and about half of the sample had committed such crimes. The prevalence of crime differed by gender and by diagnosis. More men than women committed crimes, and more schizophrenics than patients with other types of mental disorders committed crimes. However, no differences were found between the types of crime committed by subjects with different diagnoses, even though all severe violent crimes were committed by schizophrenics. Mentally disordered offenders who committed severe violent crimes were usually placed in special hospitals. 18 references and 6 tables