Diagnostic delay for endometriosis is a well-established phenomenon. Despite this, little is known about where in the health care system these delays occur or why they occur. Our review is the first attempt to synthesize and analyze this international evidence. A systematic scoping review with a pre-specified protocol incorporated the literature on diagnostic delay for endometriosis using the social-ecological theoretical framework. Four databases (PubMed, MEDLINE, EMBASE, PsychINFO) were searched from inception to September 2023. The search yielded 403 studies, 23 of which met the inclusion criteria. Most were from high-income country researchers. The average diagnostic delay reported across studies was 6.8 years (range 1.5-11.4 years) but this masked the very wide differences reported between countries. Considering the impact on individuals and the health system, addressing diagnostic delay for endometriosis must remain a priority for researchers, health care providers and policy makers.