The case of a 23-year old woman with a history of epigastric pain, a palpable tumor that covered the epigastrium and the left hypochondrium, and an episode of acute pancreatitis was reported. The computerized tomography revealed a pancreatic cyst. The CA-125 increased significantly. An exploratory laparotomy was performed, finding an endometrioma. The pathological anatomy showed necrotic tissue, mucus and blood, with a presence of macrophages with hemosiderin phagocytosis. The symptoms and signs, pathogenesis and treatment of the endometriosis of the pancreas are discussed.