The records of adolescent patients (10-21), who were admitted to the severance hospital between 1990 and 1999, were reviewed retrospectively to evaluate the age distribution, diagnosis, clinical stage, and treatment for endometriosis in adolescents. Thirty-nine patients who had undergone a laparotomy or laparoscopy and were diagnosed with endometriosis were identified. Endometriosis was classified according to the revised American Fertility Society classification (AFS). The chief symptoms leading to the diagnosis, clinical stage, age distribution, and treatment modality were reviewed. All patients, whose average age of menarche was 14.2, were diagnosed with endometriosis with an average interval of 5.9 years after menarche. The chief symptoms leading to the diagnosis were chronic pelvic pain (27%), acute pelvic pain (21%), a palpable pelvic mass (21%), and dysmenorrhea (18%). A laparoscopy was performed in 20 (51%). The majority of patients (44%) presented with the revised AFS classification stage II. Four patients (10%) presented with stage I, 11 (28%) with stage III and 7 (18%) with stage IV. Management after surgery included GnRH agonists (64.1%), expectant managements (25.7%), OCPs (5.1%) and danazol (5.1%). In adolescents with chronic pelvic pain, endometriosis is not rare. Therefore, early referal to a gynecologist to diagnose the etiology of the pelvic pain and initiate appropriate therapy is recommended.