Purpose. Further to evidence of the successful application of cognitive skills programmes with offenders in HM prison service, the Enhanced Thinking Skills (ETS) training course is now delivered in various secure forensic hospitals, and its usefulness with an offender patient population merits examination. Our aim was to evaluate the impact of ETS using measures designed to capture change in key areas targeted by the course, and a more global measure of mental well-being.Methods. Offender patients (N ¼ 83) referred for ETS between 2001 and 2006 via a wider groupwork service within a high security hospital were administered questionnaires before and after the training course, which was minimally adjusted to meet the needs of the patient population. Attendance rates, including 'drop-out' (completion of 10 or less sessions) were recorded. Demographics by subgroup (completers vs. non-completers), and the clinical significance of any changes endorsed by participants post-group were examined.Results. ETS completers were significantly more likely than non-completers to endorse changes in thinking style (e.g. a reduction in post-course scores). Significant differences were observed at both the group and individual level in the direction of less externalization of blame, a slight increase in tolerance of frustration, an increase in social conformity, and improvement in critical reasoning skills. Furthermore there was a reduction in the endorsement of aggressive solutions to social problems.Conclusions. These findings demonstrate a significant short-term impact of the course for mentally disordered offenders with regards change in aspects of their thinking style and enhancement of their social problem solving skills. This profile lends some support to the provision of ETS within secure hospital settings.