The relationship between anger, violence and offending is not well understood; there is debate in the current literature regarding the nature of this relationship. This issue is of importance because of the widespread use of anger management programmes as a means to reduce anger-mediated offending. This study specifically examined the role of anger in offending behaviour for patients with coexisting problems with anger and psychosis. Grounded theory was used to analyse patients’ file data from an Anger Management and Emotion Regulation programme in a Medium Secure Unit. Grounded theory analysis allowed for a theory of offending to be generated, showing what concepts contribute to offending and thereby determining the role anger plays in offending in mentally disordered patients. Anger, mental illness, substance misuse and social issues were recognised as contributing factors to offending behaviour. This provides justification for managing anger in order to prevent reoffending.