BackgroundIn‐prison violence by detainees is a problem worldwide, but despite evidence of a much higher prevalence of a range of psychiatric disorders than in the general population, little is known about psychopathology among violent detainees.AimsOur aim was to explore the psychopathology and mental healthcare history of Dutch detainees who were transferred to the highly restrictive facility for uncontrollably violent detainees following severe in‐prison violence.MethodsAnonymised data for all 253 male detainees incarcerated at any time between January 2016 and January 2020 in the specialist national facility for those seriously violent while in prison—‘the Violence Facility’—were obtained from the Dutch Ministry of Justice together with similarly recorded data for a matched comparison group of 253 detainees admitted to an in‐prison psychiatric facility—‘the Psychiatric Facility’.ResultsThere was no record of any psychiatric assessment for 29% of the Violence Facility men. Almost all of the detainees who had been assessed were classified with at least one disorder. Compared to detainees in the Psychiatric Facility, Violence Facility men were more likely to be diagnosed with attention deficit hyperactivity disorder (ADHD), anxiety, behavioural and personality disorders; Psychiatric Facility men were more likely to be diagnosed with psychosis or substance use disorder. Most men in both groups had previously used mental health services.ConclusionsThis first study of detainees in the Dutch in‐prison facility for violent detainees raises questions about whether the extent of violence among these men may have masked mental healthcare needs and leads to questions about potential benefits from establishing more systematic mental health assessments for them, and a need for more specialist services.