Across studies, the percentage of individuals reporting regularly engaging in menstrual coitus ranges between 4% and 43%. Although no clinical guideline recommends avoiding sexual activity during menstruation, according to some researchers such practice may favor both retrograde menstruation and sexually transmitted diseases, two phenomena that are thought to play a role in endometriosis' pathogenesis. Given this background, we analyzed the existing evidence regarding the association between menstrual coitus and the prevalence of endometriosis by conducting a PubMed database search on February 15, 2024. We considered all original, full-length studies written in English. Results were conflicting. When interviewing 489 infertile women, Filer and Wu found that the frequency of surgically diagnosed endometriosis was significantly higher among those engaging in menstrual coitus (17.5% versus 10.9%