IntroductionEndometriosis can cause chronic pain and subfertility thereby negatively affecting quality of life (QoL). Surgical removal of endometriosis lesions leads to improved health-related QoL, although not to the level of QoL of healthy controls. Pain intensity and cognitions regarding pain can play a crucial role in this health-related QoL following surgical treatment. Cognitive behavioural therapy (CBT) is a psychological treatment. In patients with chronic pain caused by a variety of medical conditions, CBT is effective in improving QoL. We designed a research protocol to investigate the effect of CBT on QoL in patients with endometriosis-associated chronic pain who are undergoing surgery.Methods and analysisThis is a study protocol for a randomised controlled trial in which 100 patients, undergoing endometriosis removal surgery due to endometriosis-associated chronic pain, will be randomised between post-surgery usual care with CBT and post-surgery usual care only. Participants in the CBT group will additionally receive seven sessions of CBT, focused on expectancy management, cognitions regarding pain and emotional and behavioural impact of pain. To determine the primary outcome Quality of life, both groups will complete questionnaires assessing QoL. The secondary outcomes pain intensity, pain cognitions, fatigue and perceived stress are also measured using questionnaires. Additionally, a marker for stress (cortisol extracted from a hair sample) will be assessed at T0 (baseline assessment), T1 (post-intervention; 2 weeks after completion of all CBT sessions) and T2 (follow-up; 14 weeks after T1). Statistical analysis will be performed using SPSS software.Ethics and disseminationThe study protocol has been approved by the Medical Ethical Committee of the region Arnhem-Nijmegen from the Radboud University Medical Centre on 2 September 2020. The findings of this study will be published in scientific journals and will be presented at scientific conferences.Trial registration numberNCT04448366.