Many people with intellectual disabilities find it hard to control their anger and this often leads to aggression which can have serious consequences, such as exclusion from mainstream services and the need for potentially more expensive emergency placements.

To evaluate the effectiveness of a cognitive–behavioural therapy (CBT) intervention for anger management in people with intellectual disabilities.

A cluster-randomised trial of group-based 12-week CBT, which took place in day services for people with intellectual disabilities and was delivered by care staff using a treatment manual. Participants were 179 service users identified as having problems with anger control randomly assigned to either anger management or treatment as usual. Assessments were conducted before the intervention, and at 16 weeks and 10 months after randomisation (trial registration: ISRCTN37509773).

The intervention had only a small, and non-significant, effect on participants' reports of anger on the Provocation Index, the primary outcome measure (mean difference 2.8, 95% Cl −1.7 to 7.4 at 10 months). However, keyworker Provocation Index ratings were significantly lower in both follow-up assessments, as were service-user ratings on another self-report anger measure based on personally salient triggers. Both service users and their keyworkers reported greater usage of anger coping skills at both follow-up assessments and keyworkers and home carers reported lower levels of challenging behaviour.

The intervention was effective in improving anger control by people with intellectual disabilities. It provides evidence of the effectiveness of a CBT intervention for this client group and demonstrates that the staff who work with them can be trained and supervised to deliver such an intervention with reasonable fidelity.