Endometriosis is a chronic gynaecological condition which has been referred to as the ‘missed disease’ due to its unclear aetiology and inconsistencies in its diagnosis and management. Unlike other long-term conditions such as diabetes and asthma, endometriosis has remained largely ignored in government policy and research funding globally. Drawing on scholarship from the growing field of ‘ignorance studies’, this paper considers how ambiguity around endometriosis is part of a wider constellation of discursive, material and political factors which enrol certain forms of knowledge whilst silencing, ignoring or marginalizing other forms of knowledge. It uses concepts of ‘undone science’ and ‘wilful ignorance’ to explore how an absence of knowledge on endometriosis is a result of structural, cultural and political processes and forces which privilege certain voices and communities. This paper suggests that the association of endometriosis with historically specific constructions of menstruation and women's pain has informed contemporary imaginaries around the condition, including ideas about women being somehow accountable for their own illnesses. Applying an ignorance lens demonstrates how the legacy of invisibility of endometriosis shapes its place in the present political and social arena, and is reflective of a process of undone science. The paper concludes by arguing that the social and political significance of endometriosis as a chronic, life-limiting condition which affects millions of women globally continues to need attention, illumination and critique. © 2021