In Tunisia, estimation of the percentage of the mentally ill among the prisoners and the most severe psychiatric pathologies has been the object of only a fewstudies. However, it seems that this population is increasing. In spite of the difficulties inherent to the data collection, these studies are essential to adapt psychiatric care. The aim of our study was to estimate the prevalence of the ... [Show full abstract] mental disorders among detainees, describe the clinical, evolutionary and therapeutic situation, assess these disorders as well as the link between the prison and the mental pathology. Thids is cross-sectional study, conducted in 2013, with mentally ill inmates in the civil prison of Mahdia. One hundred and two mentally ill prisoners answered the questionnaire. The prevalence of mental disorders in the prison was 10.12%. Prisoners had an average age of 33.3 years, the majority single (65.7%), a low level of education in 75% of cases. Murder followed by assault and injury, then rape were the most common offenses with respective rates of 41, 22 and 15%. The substance-related disorders were observed in 46% of the cases and schizophrenia was only found in 7% of the cases. A total of 47% of the patients had a psychopathic personality disorder. Our analytical study found a strong correlation between the existence of a criminal record and addictive behavior, and between violent crime and schizophrenia on the one hand addictive behavior on the other. The results of this study suggest that several factors shouldbe reviewed that reflect the proportion of psychiatric disorders in prisons: the tendency towards patient's responsibility, the effects of deinstitutionalization, the association between severe psychiatric disorders and violent behavior and comorbidity.