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