Objective. To report a case of Mayer-Rokitansky-Küster-Hauser syndrome (MRKH) in which there were two nonfunctional rudimentary uteruses with the presence of ovarian endometrioma, corroborating that there are valid alternative theories to the existence of endometriosis, rather than Sampson's theory alone, such as the coelomic metaplasia theory. Design. A case report. Setting. A tertiary referral center, which is also a university hospital. Patient. A fifteen-year-old patient with MRKH syndrome and endometriosis. Intervention. Laparoscopic approach for diagnostic confirmation and treatment of the endometrioma. Results. Evidence of endometriosis in a patient with no functional uterus. Conclusions. This case report and a few others that are available in the literature reinforce the possibility that coelomic metaplasia could be the origin of endometriosis. Patients with müllerian agenesis and pelvic pain should be carefully evaluated, and the presence of pelvic endometriosis should not be excluded.