Ectopic endometrial tissue is found in 1.5% to 6.2% of women of reproductive age, in up to 60% of those with dysmenorrhoea, and in up to 30% of women with subfertility, with a peak incidence at around 40 years of age. However, symptoms may not correlate with laparoscopic findings.We conducted a systematic review and aimed to answer the following clinical questions: What are the effects of hormonal treatments given at diagnosis of endometriosis? What are the effects of hormonal treatments before surgery for endometriosis? What are the effects of non-hormonal medical treatments for endometriosis? What are the effects of surgical treatments for endometriosis? What are the effects of hormonal treatment after conservative surgery for endometriosis? What are the effects of hormonal treatment after oophorectomy (with or without hysterectomy) for endometriosis? What are the effects of treatments for ovarian endometrioma? We searched: Medline, Embase, The Cochrane Library, and other important databases up to December 2009 (Clinical Evidence reviews are updated periodically, please check our website for the most up-to-date version of this review). We included harms alerts from relevant organisations such as the US Food and Drug Administration (FDA) and the UK Medicines and Healthcare products Regulatory Agency (MHRA).We found 40 systematic reviews, RCTs, or observational studies that met our inclusion criteria. We performed a GRADE evaluation of the quality of evidence for interventions.In this systematic review we present information relating to the effectiveness and safety of the following interventions: combined oral contraceptives, danazol, dydrogesterone, gestrinone, gonadorelin analogues, aromatase inhibitors, hormonal treatment before surgery, hormonal treatment, laparoscopic cystectomy, laparoscopic removal of endometriotic deposits (alone or with uterine nerve ablation), laparoscopic removal plus presacral neurectomy, laparoscopic uterine nerve ablation, non-steroidal anti-inflammatory drugs, presacral neurectomy alone, and progestogens other than dydrogesterone.