Operationalized risk factors (OPRISK) make the evidence for mentally disordered offenders’ (MDOs) security needs explicit, aiding communication across service settings and improving access to care. Receiver operating characteristic curves of the predictive validity of OPRISK yielded an area under the curve of 0.765. Internal consistency (>0.75) and inter-rater reliability (0.925) were high. This work sought to assess the predictive validity and reliability of a structured assessment of security need (OPRISK) in a prospective cohort of referrals to a high security hospital. It was noted that more mentally disordered offenders (MDOs) were referred to secure psychiatric care settings than were accepted for admission, and that psychiatrists working in different care settings might disagree on the appropriate level of security for MDOs, resulting in treatment delay. The work also notes that a preadmission structured assessment of security needs for MDOs may facilitate agreement and access to care. Data were derived from operationalized criteria describing risk factors related to security need which were used to develop OPRISK, an 18-item checklist. The predictive validity of OPRISK was assessed prospectively on the outcome of 140 referrals to Broadmoor, a high security hospital in the United Kingdom. Figures, tables, references, and appendices