Anger and aggression are prevalent problems among people with developmental disabilities and constitute primary reasons for them to be admitted and re-admitted to institutions. They are also a key reason for the prescribing of behaviour control and anti psychotic medication to this client group. Stimulated by growing research in this area, mental health and criminal justice professionals have begun to see the benefits of anger assessment and cognitive behavioural anger treatment for people with developmental disabilities. There is no prior text to guide anger treatment provision to this client group. This text presents a manual guided cognitive behavioural anger treatment protocol, grounded in a solid theoretical framework and empirical evidence for its efficacy in clinical practice. The assessment and treatment approach is designed to engage and motivate patients with recurrent and deep rooted anger problems and their manifestation in serious aggressive behaviour. Accompanying the treatment protocol are a number of worksheets, handouts, and exercise sheets for clinicians and clients that can be accessed online.