**Abstract**

Endometriosis is a serious, often irreversible disease of the mare. Often associated with endometritis, this chapter will review our current understanding of pathophysiology, etiology, diagnosis and possible treatments. Endometriosis is a disease complex typically seen in our older mare population. It is important that we understand that although the same term is used to describe a condition in our human patients, it is, however, not the same medical condition as seen in our equine patients. As this disease profile is irreversible with limited treatment options, it causes significant economic strain in our broodmare population.

**Keywords:** mare, uterus, endometriosis, endometritis, infertility
