This study assesses the feasibility of a cognitive-behavioural group programme for treating anger and aggressiveness after a traumatic brain injury (TBI). Five feasibility criteria were considered: demand, implementation, practicality, acceptability and initial efficacy. A self-report questionnaire of aggressiveness (AQ-12) was administered before the intervention (T1), one week following the intervention (T2) and at a four months follow-up (T3). Ten patients with moderate to severe chronic TBI completed the programme through eight once-a-week sessions. The analysis of the feasibility outcomes suggests that: (1) The recruitment, the process of grouping participants and the characterisation of anger and aggressiveness at baseline need to be re-evaluated and improved for future designs. (2) The use of specific strategies for bypassing cognitive and other behavioural dysfunctions related to TBI is crucial for the success of this intervention and merits special attention. (3) The high retention rate, the convenient meeting schedule, cost advantages and the good acceptability by participants are positive arguments for the implementation of a larger trial. (4) The significant reduction of AQ-12 scores at T3 and the high effect size constitute a change in the expected direction and support the initial efficacy of the programme.