Sections 47 and 48 of the Mental Health Act 1983 allow prisoners to be transferred from prison to an appropriate health-care setting in order to be treated. There is an awareness that delays exist when transferring prisoners to hospital. However, literature regarding the delay in returning these patients from hospital is limited. The admissions from prison to a Psychiatric Intensive Care Unit (PICU) in South West London were compared to non-offenders on the PICU in order to compare the average length of stay for both groups and the time taken for the discharge from PICU once felt clinically appropriate. The study also compared demographic profiles, reason for admissions, psychiatric diagnosis and index offences. Over six years, there were 18 admissions from prison to a PICU. The control group comprised 37 non-offenders admitted to the same PICU. On average the prison group took longer to be deemed clinically ready for discharge and, even once clinically ready, then took longer to be discharged. The average length of stay in PICU was 77.83 days for prisoners, and 16.46 days for non-offenders. All 55 admissions were between 1 January 2008 and 31 December 2014. The offender pathway and the difference in the length of stay between prisoners and non-offenders in a PICU warrants further exploration. Possible recommendations to reduce the length of stay of prisoners include improved information sharing between prisons and hospital, and clearer guidelines regarding the level of security required.