BACKGROUND: Endometriosis-associated pain and dyspareunia influence female sexuality, but little is known about men's experiences in affected couples. AIM: To investigate how men partners experience sexuality in partnership with women with endometriosis. METHODS: A multi-center case-control study was performed between 2010 and 2015 in Switzerland, Germany, and Austria. 236 Partners of endometriosis patients and 236 partners of age-matched control women without endometriosis with a similar ethnic background were asked to answer selected, relevant questions of the Brief Index of Sexual Functioning and the Global Sexual Functioning questionnaire, as well as some investigator-derived questions. OUTCOMES: We sought to evaluate sexual satisfaction of men partners of endometriosis patients, investigate differences in sexual activities between men partners of women with and without endometriosis, and identify options to improve partnership sexuality in couples affected by endometriosis. RESULTS: Many partners of endometriosis patients reported changes in sexuality (75%). A majority of both groups was (very) satisfied with their sexual relationship (73.8% vs 58.1%, P = .002). Nevertheless, more partners of women diagnosed with endometriosis were not satisfied (P = .002) and their sexual problems more strongly interfered with relationship happiness (P = .001) than in partners of control women. Frequencies of sexual intercourse (P < .001) and all other partnered sexual activities (oral sex, petting) were significantly higher in the control group. The wish for an increased frequency of sexual activity (P = .387) and sexual desire (P = .919) did not differ statistically between both groups. CLINICAL TRANSLATION: There is a need to evaluate qualitative factors that influence sexual satisfaction in endometriosis patients. CONCLUSIONS: This is one of the first studies to investigate male sexuality affected by endometriosis. The meticulous verification of diagnosis and disease stage according to operation reports and histology allows for a high reliability of diagnosis. Our men's response rate of almost 50% is higher compared to other studies. Recruiting men through their woman partner may have caused selection bias. The adjustment to the specific situation in endometriosis by selecting questions from the Brief Index of Sexual Functioning and Global Sexual Functioning and adding investigator-derived questions likely influenced the validity of the questionnaires. Despite the fact that both partners of endometriosis patients and of control women largely reported high sexual satisfaction, there are challenges for some couples that arise in the context of a sexual relationship when one partner has endometriosis. Challenges such as sexuality-related pain or a reduced frequency of sexual activities should be addressed by health care professionals to ameliorate any current difficulties and to prevent the development or aggravation of sexual dysfunction. Hämmerli S, Kohl Schwartz AS, Geraedts K, et al. Does Endometriosis Affect Sexual Activity and Satisfaction of the Man Partner? A Comparison of Partners From Women Diagnosed With Endometriosis and Controls. J Sex Med 2018;15:853-865.