Background: This is the first epidemiologically representative cross-sectional study of psychiatric morbidity using research diagnostic instruments in sentenced prisoners in Ireland.

Objective: To estimate the prevalence of psychiatric morbidity and psychiatric service requirements.

Method: We interviewed 340 men serving a fixed sentence (14.6% of total) and 98 men serving a life sentence (82% of total). Prisoners were drawn from 15 different prisons using a random stratified sampling method. Mental illness and substance misuse was measured using the SADS-L, SODQ and a structured interview to generate ICD-10-DCR diagnoses.

Results: We found a high prevalence of mental illness. Our six month prevalence for psychosis (2.7%) was similar to an international meta-analysis. We found a significantly higher prevalence of psychosis in life sentenced prisoners (6.1%) compared to fixed sentenced prisoners (1.8%). Drugs and alcohol problems were very prevalent.

Conclusions: Using the six month prevalence figures found for psychosis, we estimate that there are approximately 79 sentenced male prisoners with a severe mental illness who would require treatment in hospital additional to current provision. We discuss the relationship between drug availability and the prevalence of severe mental illnesses in prisons.