WHAT IS KNOWN ON THE SUBJECT? : International reviews have looked at therapy outcomes for patients on mental health wards, showing it is associated with reduced emotional distress and readmission. Reviews have not looked at which specific treatments are most effective. No review has been done in England and Wales for patients detained specifically under the Mental Health Act. The paper gives an overview of the limited evidence in England and Wales. The paper shows which therapies have been measured. WHAT ARE THE IMPLICATIONS FOR PRACTICE? : Larger studies are needed across all types of patient wards in England and Wales with random allocation to types of therapy and longer-term follow-up. More studies are needed where researchers are not aware of the therapy being delivered. More studies need to use a mixture of patient and clinician outcome measures. Outcomes should also measure incident, readmission and reoffending rates. More evidence is needed from patients who are female, non-white and who are diagnosed with depression and anxiety. INTRODUCTION: The efficacy of psychological interventions delivered under the Mental Health Act (1983) (MHA) in England and Wales is unclear. While meta-analyses have reviewed acute and forensic psychological interventions in wider geographical areas, there has been no review specifically in the unique MHA context. A systematic review was conducted of psychological outcomes for inpatients detained under the MHA in England and Wales. Diagnoses and type of psychological intervention were not restricted, provided a psychological outcome measure was used. Studies were identified through APA PsychInfo, MEDLINE, CINAHL and Academic Search using a combination of key terms. Data extraction included effect direction, statistical significance, intervention type, format and duration, study size, inpatient setting, control group and study quality. High-quality evidence was sparse. Some improvements were found in overall well-being, self-esteem, social functioning, problem-solving, substance use, anger, offending attitudes, fire-setting, violence, anxiety, depression, personality disorder and psychosis. However, the overall evidence base is lacking. Larger-scale randomized controlled trials are needed across secure, acute and learning disability inpatient settings in England and Wales with longer term follow-up, blind assessors and both self-report and clinician-rated measures, as well as incident, readmission and reoffending rates. Greater representation is needed of females, non-white groups and affective disorders. The efficacy of psychological interventions for inpatients detained under the MHA in England and Wales remains unclear. Clinicians are encouraged to use relevant outcome measures in relation to treatment goals, to monitor the efficacy of interventions being offered to this client group. This paper highlights the current body of evidence for psychological interventions in inpatient settings within England and Wales, which is an environment in which mental health nursing plays an important role in patients' recovery. This evidence is also particularly important as there is a shift in clinical practice to training nursing staff to deliver some of the low-intensity psychological interventions, such as behavioural activation, solution-focussed therapy and motivational interviewing.