Abstract Study question In this previous undescribed population of women, what is the prevalence of endometriosis and associated symptomatology, and how are women affected? Summary answer Prevalence of endometriosis was 5.4% (95%CI; 4.9%-5.9%). Cases suffered from worse physical health, higher use of pain medication and decreased productivity at work. What is known already There is a lack of population level data on prevalence and distribution of women’s health conditions, such as endometriosis, from the Eastern Mediterranean region, despite their known negative effects on quality of life. In addition, there is a complete absence of any health statistics from Northern Cyprus, an emerging region in Europe. Most current endometriosis research comes from Western populations and is not generalisable to non-Western populations due to differences in culture, lifestyle, and care seeking patterns. Therefore, it is important to investigate endometriosis in a variety of settings. Study design, size, duration The COHERE Initiative is a cross-sectional, population-based study that recruited 7,646 women between the ages 18-55 residing in Northern Cyprus between January 31st 2018, and January 31st 2020. Recruitment took place face-to-face (90%) and online (10%). Participants completed an expanded version of the WERF Endometriosis Phenome and Biobanking Harmonisation Project (EPHect) questionnaire, consisting of previously validated measurement instruments, such as the Short-Form-36-version-2 questionnaire (SF-36v2) and the Work Productivity and Impairment Questionnaire: General Health (WPAI:GH). Participants/materials, setting, methods Endometriosis cases were defined using a combination of self-reported and pelvic ultrasound data. Controls were women without endometriosis. Chi-square, Fisher’s exact test, Student’s t-test, linear regression, and multivariable logistic regression were used for data analysis. The significance level was set at p < 0.05. Main results and the role of chance Endometriosis prevalence was 5.4% (95%CI; 4.9%-5.9%;n=410). The mean age women with endometriosis reported to first experience related-symptoms was 25.9-years, despite average age of first menstrual-pain occurring at 16.2-years. Average age of first gynaecologist visit was 21.0-years and endometriosis diagnostic-delay was 1.5-years. Physical health-related-quality-of-life was lower in women with endometriosis compared to those without (48.4 vs 50.2, p = 0.001). Cases had a higher mean percentage of activity impairment (25.8% vs 22.5%, p = 0.03) and reduced effectiveness whilst working (23.4% vs 19.5%, p = 0.006) than controls. Hormone-use was higher in women with endometriosis compared to controls for heavy-bleeding (5.9% vs 1.4%, p < 0.001), irregular periods (14.4% vs 7.2%, p < 0.001) and pelvic-pain (9.3% vs 1.7%, p < 0.001), though overall hormone use was low at 24.1%. Iron and vitamin-D deficiency were the most reported co-morbidities, and these proportions were significantly different from women without endometriosis (38.8% vs 28.3%, 23.9% vs 17.0% respectively, p < 0.001). Migraine headaches were more frequent in women with endometriosis than in those without (19.8% vs 13.2%, p < 0.001). Women with endometriosis were more likely to have ever used drugs for pain relief (77.1% vs 60.5%, p < 0.001). Further analysis will include estimation of economic burden of endometriosis and investigation into Mediterranean-specific factors including sun-exposure and dietary-habits. Limitations, reasons for caution Given the cross-sectional nature of this study, causality cannot be inferred. The majority of endometriosis cases are self-reported which is not as reliable as hospital diagnosis/surgeries and laparoscopy is not available in Northern Cyprus. However, research has shown that women self-report endometriosis diagnoses with reasonable accuracy (>70%). Wider implications of the findings This is the first study that has estimated prevalence of endometriosis in the region and provided insight into the current-status of healthcare. It has highlighted gaps in the public’s general knowledge of common gynaecological conditions. The results form the basis for targeted follow-up-studies and promotes evidence-based reproductive-medicine in the Eastern-Mediterranean-region. Trial registration number Not applicable