During the past 40 years there has been an increase in the number of mentally ill criminals. The purpose of this study is to analyse the correlations between the reorganisation of the psychiatric treatment system the growing number of forensic patients and the increase in serious crime, homicide and arson associated with the mentally ill.

We estimated the annual positive or negative growth rate of consumed psychiatric beds and in social and community psychiatry (explanatory variables) and in prevalence and incidence of forensic patients, homicide and arson (response variables) from 1980 to 1997 for each of the 14 Danish counties. The long-term effect was analysed in the form of between-county analysis with both single and multiple regressions.

Bed closure had no immediate effect on either the number of forensic patients or serious criminality. Over time the (negative) growth rate in number of consumed beds is significantly correlated with the (positive) growth rates for forensic patients, homicide and arson. Social and community psychiatry have little effect, if any.

We have used two sets of data firstly the number of forensic patients and, secondly the reported number of crimes associated with the mentally ill. The uniformity of the results leads us to consider that the decreasing effort invested in inpatient treatment is causing an increase in the crime rate among the mentally ill.

Forensic patients are not only offenders, but also the victims of an inadequate treatment system. Modern inpatient treatment facilities should be established.