Background Psychiatric morbidity in prisons and police custody is well established, but little is known about individuals attending criminal court. There is international concern that vulnerable defendants are not identified, undermining their right to a fair trial. Aims To explore the prevalence of a wide range of mental disorders in criminal defendants and estimate the proportion likely to be unfit to plead. Method We employed two-stage screening methodology to estimate the prevalence of mental illness, neurodevelopmental disorders and unfitness to plead, in 3322 criminal defendants in South London. Sampling was stratified according to whether defendants attended court from the community or custody. Face-to-face interviews, using diagnostic instruments and assessments of fitness to plead, were administered (n = 503). Post-stratification probability weighting provided estimates of the overall prevalence of mental disorders and unfitness to plead. Results Mental disorder was more common in those attending court from custody, with 48.5% having at least one psychiatric diagnosis compared with 20.3% from the community. Suicidality was frequently reported (weighted prevalence 71.2%; 95% CI 64.2-77.3). Only 16.7% of participants from custody and 4.6% from the community were referred to the liaison and diversion team; 2.1% (1.1-4.0) of defendants were estimated to be unfit to plead, with a further 3.2% (1.9-5.3) deemed 'borderline unfit'. Conclusions The prevalence of mental illness and neurodevelopmental disorders in defendants is high. Many are at risk of being unfit to plead and require additional support at court, yet are not identified by existing services. Our evidence challenges policy makers and healthcare providers to ensure that vulnerable defendants are adequately supported at court.

Original languageEnglish
Article numbere92
JournalBJPsych Open
Issue number3
Publication statusPublished - 12 May 2022


  • Developmental disorders
  • forensic mental health services
  • human rights
  • psychiatry and law
  • psychotic disorders


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