Purpose Endometriosis of the vermiform appendix is an uncommon pathology that may present as an appendiceal mass identified on colonoscopy. Mucinous appendiceal neoplasms and neuroendocrine tumours are important clinical differentials. When there is concern for possible malignancy, resection is recommended. Methodology In this case we describe an appendiceal endometrioma presenting as an appendiceal mass, requiring a right hemicolectomy. Results A 40-year-old female was referred to a colorectal surgeon for workup of altered bowel habits on a background of endometriosis. A colonoscopy was performed revealing an abnormal appendiceal orifice with an intraluminal protruding mass suspicious for an appendiceal mucinous neoplasm. To obtain a tissue diagnosis the patient was planned for laparoscopic caecectomy. Intraoperative findings included a short appendix and a firm caecal base suspicious for malignancy. A partial caecectomy was unable to be performed with appropriate margins and a right hemicolectomy was performed instead with side-to-side stapled ileocolic anastomosis. Microscopic examination of the resected appendix revealed multiple foci of endometriosis within the appendix and mesoappendix. There was no neoplasia identified. Conclusion Differentials for an appendiceal mass include endometriosis, malignancy and appendiceal intussusception. Endometriosis may exist concurrently with appendiceal neoplasm, or an appendix that macroscopically appears consistent with endometriosis may represent malignancy. Therefore, surgical resection is the recommended treatment for an appendiceal mass.