Ectopic endometrial tissue is found in 2% to 6% 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 question: What are the effects of dienogest for the treatment of endometriosis? We searched: Medline, Embase, The Cochrane Library, and other important databases up to June 2014 (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).Five studies were included. 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: dienogest versus placebo or no treatment; dienogest versus gonadorelin analogues; dienogest versus combined oral contraceptives; dienogest versus other progestogens.