**1. Introduction**

This chapter will examine endometriosis in our equine patients, focusing on etiology, diagnosis/prognosis and treatments for this debilitating condition. Endometriosis in the mare is a multifactorial disease, with severity of endometriosis being positively correlated with age. This condition, although with the same name given to a condition seen in women, is not the same in nature, pathophysiology and/or treatment. A detailed comparison between the condition seen in our equine patients and that of women is given below. Further it is utmost important for the scholars amongst us to be aware of the differences between endometritis and endometriosis; although similar and indeed as will be shown, often linked, they again are different conditions. For clarity, endometritis relates to the inflammation of the endometrium, either of an infectious nature (typically bacteriologic) or noninfectious, such as the presence of spermatozoa in the uterine lumen. Whereas endometriosis in the mare is characterized by chronic endometrial degeneration. This condition has serious consequences from an economic standpoint and often leads to mare being infertile.
