ABSTRACT The neuropsychological assessment of individuals with a mental disorder and deemed to be a ‘grave and immediate’ risk of harm to others admitted to one UK high-secure psychiatric care (HSPC) hospital makes an important contribution to the formulation of their difficulties and treatment needs. Included within the assessments is the DEX S questionnaire, assessing the subjective experience of any executive dysfunction (ED). An examination of 205 DEX S profiles suggests ED is common, particularly among younger individuals and with no difference between those who self-report a history of head injuries. Whilst a non-clinical non-forensic classification system suggested 43.9% of individuals fall into a ‘high deficit’ category and 24.4% fall into a ‘moderate deficit’ category, a HSPC classification system suggests higher thresholds, with 22.4% and 33.2% falling in ‘high deficit’ and ‘moderate deficit’ categories, respectively. Frequently endorsed items are associated with difficulties understanding others unless things are kept simple and straightforward, acting without thinking, expressing emotions, feeling restless, and problems sitting still for any length of time and being easily distracted. Results are discussed in terms of increasing awareness of ED among those involved in the care of mentally disordered offenders, cognitive remediation and the potential for a forensic psychiatric version of the DEX.