Endometriosis has been reported in humans, great apes, and Old World monkeys. Although cases are noted anecdotally in Mandrillus spp., and a previously reported case was noted on postmortem examination, to the authors' knowledge, no previous reports of case management have been published in the peer-reviewed literature. This paper describes the medical and surgical management of endometriosis in two mandrills (Mandrillus sphinx).