Transcutaneous Electrical Nerve Stimulation for Endometriosis-related Chronic Pain

Inclusion Criteria: * Age ≥18 years * Consents to participation in the study * Verified endometriosis (by laparoscopy or ultrasound). * Chronic endometriosis-related pain (\> 3 months), available for TENS treatment * Functioning, stable endometriosis-specific hormonal drug therapy. The endometriosis-specific drug therapy must be unchanged for the last 3 months and no gynecological surgical procedures for the treatment of endometriosis are planned during the next 7 months (during study participation). The endometriosis-specific drug therapy does not refer to analgesic therapy for symptom relief of endometriosis-related pain. Exclusion Criteria: * Patient with inability to understand and use written and spoken Swedish * Patient with pacemaker and/or ICD or other electronic implants * Patient with impaired sensation over the painful area * Malignant disease with an expected survival \<12 months * Alcohol or substance abuse * Serious untreated psychiatric illness and/or psychological condition that is the primary determinant of the patient's condition * Participating in another intervention study with possible impact on current study outcome measures * Patient who is using \>90 morphine equivalents/day * Patient who is electro-acupuncture * Pregnancy