A research-action program was established in 1996 between the Loos- Lez-Lille prison psychiatric unit and the Department of Medical Informatics of the University Hospital of Lille (France) : - (1) to investigate the health status and the general characteristics of the prison population - (2) to develop an Information System for improving the prison health care and to facilitate social rehabilitation of convicts. Starting off 1988, all new prisoners are interviewed on their arrival using a standard questionnaire. The transfer of all the information recorded in this questionnaire into a computer base was initiated in 1996, when the research action program began. A statistical analysis was performed on 15200 records (1989-1995) to identify the most informative parameters : 50% of inmates were less than 24 years old; 57% were unemployed; 60% had no professional qualification. 31% of inmates had a psychiatric history and 16% had made a previous suicide attempt. The rate of drug abuse has increased from 24% in 89 to 53% in 95. To analyze the time trends of these parameters, a prototype of Information System was then developed. The system uses the database to product standard reports in real time.