The appendix mucocele is a rare disease. Sometimes it is discovered accidentally and sometimes resembles acute appendicitis. The correct diagnosis before surgery is important for the selection of adequate surgical treatment to avoid intraoperative and postoperative complications. Ultrasonography, and particularly computed tomography (CT), should be widely used for this purpose. If the mucocele is treated incorrectly, the peritoneal pseudomyxoma may develop. We report a case of appendicular mucocele in a 60-year-old male patient who was admitted to the emergency department of the Military Hospital Mohamed V in Rabat with signs of acute appendicitis. Because it is an elderly patient, in whom the literature insists on the performance of CT, this technique evidenced the diagnosis. Right hemicolectomy was performed through open emergency surgery and a termino-lateral anastomosis because the base of the appendix was involved in the process. No free fluid was found in the peritoneal cavity. The histopathological diagnosis was the mucocele of the appendix with simple mucosal cyst. The patient has been in regular follow up since 2006.