High secure forensic inpatient hospitals serve important functions in the detention and rehabilitation of people with serious mental health needs who present as a risk to society.Establishing whether services are effective in restoring mental health and reducing risk is an important task, but one that has not been systematically undertaken. A systematic review of outcome evidence from this setting was therefore conducted to establish its scope and quality.Evidence was found from twenty-two studies for nine different interventions targeting multiple and overlapping outcomes, which included recidivism, mental health, aggression, social functioning and quality of life. Studies were commonly assessed as being at a potentially high risk of bias from validity threats. The 'best' available evidence was for medication, psychoeducation and third-wave cognitive-behavioural interventions. Clinical implications are tentatively offered given the narrow focus of the review on high security. Directions for the high secure services research agenda are more definitively proposed.