Background Anger management programmes for offenders typically aim to improve the management of emotion associated with aggressive and antisocial behaviour. Such programmes have been quite extensively evaluated in prison and probation settings, but there is less published research in forensic mental health settings. Aim This study aimed to evaluate anger management groups in a high‐security hospital. Method Eighty‐six patients were referred for a 20‐session anger management intervention. Outcomes were self‐reported experiences of anger and changes in institutionally documented incidents of aggression. Incident rates were retrospectively reviewed for all group graduates, where data were available, including a comparison group of graduates who acted as their own controls. Results Group graduates reported sustained reductions in feelings of anger and positive changes in their use of aggression in reaction to provocation. Some reduction in incidents of physical aggression was noted when group completers were compared with non‐completers. Incidents of verbal aggression were observed to increase for graduates. There was also a trend towards improvement when treated men were compared with men on the waiting list. Conclusions Our findings contribute to the growing evidence for anger management groups for aggressive men, although the low‐base rate of incidents, typical of such a containing and therapeutic hospital setting, rendered the analysis of behavioural outcomes difficult. Implications for practice and research Anger management sessions for male forensic psychiatric patients can be effective in reducing incidents of physical aggression in response to provocation. Evaluation of treatments for anger is particularly difficult in secure and protective settings, where the aim is to keep incidents of actual physical aggression to a minimum. Further research of this kind is needed to test the value of self‐reported reduction in angry feelings as an indicator of clinically useful progress. Copyright © 2013 John Wiley & Sons, Ltd.