Adenomyosis is a non-neoplastic condition characterized by the presence of ectopic endometrium in the myometrium with hyperplasia of adjacent smooth muscle. Common symptoms in women include debilitating pelvic pain and abnormal uterine bleeding, and the condition has been paradoxically associated with both multiparity and subfertility. Adenomyosis spontaneously occurs in humans and some non-human primates, including the baboon and macaque, where it has been associated with primary infertility and the presence of endometriosis. No cases of adenomyosis have been previously reported in Pongidae such as gorilla, orangutan or chimpanzee. We here describe two cases of naturally occurring adenomyosis in the chimpanzee (Pan troglodytes) and briefly review the literature regarding the presence of adenomyosis in non-human primate species.