Aims and methodThere is evidence that changing diagnoses may be an important factor preceding homicide, but there is little literature on diagnostic antecedents to admission to specialist secure units after violent behaviour. Our aim was to establish the frequency of a history of changing diagnoses in patients in a UK specialist unit, and to explore the characteristics of these patients.ResultsIn total, 38 of 42 study participants had prior contact with psychiatric services. Just over 40% (16 of the 38) had had their diagnosis changed three or more times. All those who had major changes in their diagnosis had received a diagnosis of a psychotic illness at some point prior to the secure unit admission, but then had it withdrawn, only to be restored after prolonged assessment in the secure unit. Personality disorder and substance misuse comorbidity was common in this group; however, non-psychotic diagnoses were seen as more important than psychotic diagnoses by general services.Clinical implicationsChanges in diagnosis between first presentation to psychiatric services and admission to a medium-security unit were more common than would be expected from reports in the general literature. They are a testimony to the difficulties experienced by service providers in delivering a consistent service. This needs to be studied further.