Aims – To define the prevalence of mental disorder within an Italian local jail and to describe main psychiatric treatments provided. Methods – Cross-sectional study of consecutive male prisoners referred, over a twenty-month period, for a clinical psychiatric assessment, among population (N=990) of Casa circondariale “Torre del Gallo”, Pavia (I); clinical DSM-IV diagnostic assessment and retrospective analysis of provided psychiatric treatments (i.e. psychiatric visits and pharmacological prescriptions). Results – 191 men (19.3%) had one or more current mental disorders (excluding substance misuse), including 13 (1.3%) psychosis; 53 (5.4%) mood disorder; 24 (2.4%) anxiety disorder; 26 (2.6%) adjustment disorder; 40 (4.1%) personality disorder; 32 (3.2%) personality disorder plus mood disorder; 3 (0.3%) mental retardation. Substance- (N=89, 47%) and HIV-related (N=19, 10%) disorders comorbidity is recognised. Psychiatric visits are mainly provided to psychosis and personality disorder plus mood disorder subgroups. Off-label antipsychotics prescriptions are frequent. Conclusions – The prevalence of mental disorder in this population is higher than US and EU averages, and for particular diagnostic subgroups it could be underestimated. Psychiatric management in prison should be reorganized according to national and European health guidelines.