Appendicular endometriosis is a rare and poorly understood pathology that affects women in their reproductive years. In the gravid woman, ectopic endometrial tissue undergoes decidualization. This physiological process can result in acute appendicitis in exceptional cases. Here we describe a patient in her second trimester of pregnancy who presented with right iliac fossa pain and clinical, laboratory and imaging findings consistent with acute appendicitis. A laparoscopic appendectomy was performed with intraoperative findings suspicious for malignancy. Histological analysis made the surprising diagnosis of decidualized endometriosis causing luminal constriction resulting in acute appendicitis. We also detail the challenging diagnostic and management issues faced by clinicians in such cases.