BackgroundFollowing an acquired brain injury, individuals frequently experience anxiety and/or depressive symptoms. However, current treatments for these symptoms are not very effective. A promising treatment is acceptance and commitment therapy (ACT), which is a third-wave behavioural therapy. The primary goal of this therapy is not to reduce symptoms, but to improve psychological flexibility and general well-being, which may be accompanied by a reduction in symptom severity. The aim of this study is to investigate the effectiveness of an adapted ACT intervention (BrainACT) in people with acquired brain injury who experience anxiety and/or depressive symptoms.MethodsThe study is a multicenter, randomized, controlled, two-arm parallel trial. In total, 94 patients who survive a stroke or traumatic brain injury will be randomized into an ACT or control (i.e. psycho-education and relaxation) intervention. The primary outcome measures are the Hospital Anxiety and Depression Scale and the Depression Anxiety Stress Scale. Outcomes will be assessed by trained assessors, blinded to treatment condition, pre-treatment, during treatment, post-treatment, and at 7 and 12 months.DiscussionThis study will contribute to the existing knowledge on how to treat psychological distress following acquired brain injury. If effective, BrainACT could be implemented in clinical practice and potentially help a large number of patients with acquired brain injury.Trial registrationDutch Trial Register, NL691, NTR 7111. Registered on 26 March 2018. https://www.trialregister.nl/trial/6916.