Many Veterans with gastrointestinal disorders, such as inflammatory bowel disease (IBD), also have mental health conditions. IBD and mental health conditions can worsen one another through the brain-gut axis, leading to dramatic deficits in psychosocial functioning and quality of life (QOL). Yet, few Veterans with comorbid IBD and mental health conditions receive psychotherapy and no evidence-based psychotherapies have been tested in Veterans with these comorbidities. Adapting brief acceptance and commitment therapy (ACT) to the specific to the needs of these patients and embedding treatment into routine gastroenterology care may increase Veterans' access to efficient and effective rehabilitative care. This study aims to adapt and test an integrated, 1-Day ACT intervention tailored to the specific needs of Veterans with IBD and mental health conditions to improve psychosocial functioning and QOL.