The primary aim of this study is to investigate the effect of Internet-delivered Acceptance and commitment therapy for endometriosis and chronic pain. A pilot study (no randomization; N=10) will be conducted to test the intervention and assessment procedures. The participants will go through an active internet-based ACT treatment focused on education about endometriosis and chronic pain, value-based exposure for avoided situations, and behavior change through exercises targeting the processes mindfulness, cognitive defusion and acceptance. The treatment is delivered on a safe internet platform. Participants have planned telephone contact with their assigned psychologist 2 times during the program and can also contact their psychologist via a message system in the platform and expect answer within 48 hours.

Objective The primary aim of this study is to investigate the effect of Internet-delivered Acceptance and commitment therapy (iACT)for endometriosis.

Sample size 10 participants.

Trial design All participants are offered treatment. Participants are recruited from the Pain Rehabilitation Unit and the team for endometriosis at Skåne University Hospital. The unit is a government supported, regional specialist center focused on assessment and treatment of chronic pain and related disability.

Assessments Baseline and posttreatment (2 weeks after treatment) assessments will be conducted. Self-report measures will also be collected at baseline, post-treatment as well as during a 3-month follow up.

Assessment includes:Pre-and post assessment Assessors collected demographic information and self-report measures. During the pre-assessment the Mini International Neuropsychiatric Interview 5.0 (MINI) was administered to detect the presence of other comorbid disorders and assess inclusion criteria and rule out exclusion criteria.

During treatment During treatment the treatment credibility scale was administered to assess the patients' perceptions of how credible the treatment was following the introduction of the treatment rationale and the main treatment components (included in the internet program).

Safety parameters: As a mean to monitor safety and progress participants complete self-report measures (MPI, NRS, PIPS, PCS) and a question about suicidal ideation twice during the program and the therapist can follow these scores. In addition, participants can report any adverse events during treatment, at posttreatment and follow-up assessment.

Post-treatment exit interview At the post-assessment, the assigned assessor asked participants about their satisfaction with and experience of the program, what they found helpful or unhelpful and suggestions for future improvements.

Measures were taken at baseline, 2-weeks, 3 months follow-up. Self-report measures were mailed to participants

Main statistical analysis Between-group estimates on outcome will be conducted using repeated measurements. The analyses will be conducted using intention to treat principles and post hoc comparisons.

Inclusion Criteria:

• verified endometriosis
• age between 18-65 years
• were fully examined medically and had received medical treatment if indicated
• were able to be an active part of the rehabilitation process, regain functioning in different life areas and participate in treatment interventions for approximately 5 hours every week
• stable dose of medication
• able to read and write in Swedish
• had access to a smart phone or computer with internet access

Exclusion Criteria:

• had acute or severe psychiatric disorders or symptoms that warranted designation as the primary disorder (ongoing substance dependence, untreated bipolar disorder, OCD, psychotic symptoms, severe depression, PTSD)
• were actively abusing analgesic medications (including narcotics), alcohol or other drugs
• had great difficulty to harbour and handle strong emotions that could lead to emotional outbursts or self-harming behavior
• had health risks due to medical reasons;
• had social or economic difficulties or lack of social support that hindered behavior change
• current severe suicidal ideation that warranted immediate intervention (indicated by the MINI and a score of 3 to item 9 of the Patient Health Questionnaire 9-item version (PHQ9))