Study Objective: To investigate the clinical presentations, diagnosis, treatment modalities and prognosis of endometriosis in adolescents in China. Design: Retrospective study. Setting: Data were collected from records of the Peking Union Medical College Hospital from 1992-2010. Participants: This study consisted of 63 patients <= 20 years old with surgically diagnosed endometriosis. Their clinical presentations, auxiliary examinations, surgical outcomes, and post-operative medical treatments were analyzed. The follow-up information of 35 cases was collected. Results: Mean age at diagnosis was 18.41 +/- 1.84 years with a much earlier disease onset in adolescents with genital tract malformations. Of the 35 patients with follow-up time that ranged from 12-98 months, nine in 15 patients who didn't proceed with medical treatment after operation had a recurence (9/15), seven in 15 patients who took oral contraceptive pills (OCP) or progestin only pills had reoccurrence recurred (7/15), and none of the five patients received gonadotropin-releasing hormone agonist (GnRHa) therapy recurred (0/5). In this study, multiple sites lesions was defined as more than one site being involved of the following four sites: the left ovary, the right ovary, the rectovaginal pouch and the uterosacral ligament. Among the 15 cases without postoperative medical therapy, all five cases with multiple sites lesions had recurrence (5/5), while only four of the other 10 cases had relapse (4/10). The difference was of statistical significance (Fisher exact test, P = 0.044). Conclusion: Multiple sites lesions found in operation was a risk factor of recurrence. GnRHa was effective to prevent the recurrence.