An observation of a mucinous cystadenocarcinoma of the appendix, in the tumor form, revealed by a painful syndrome of the right iliac fossa in a 62-year man is reported. It is a rare malignant tumor as less than 0.5% of the appendicectomy parts present a malignant mucosecreting tumor. In our observation, the diagnosis was allowed by pre-operation imaging. An increase of the serous amount in the tumor markers (carcinoembryonic antigen) (CEA) and CA 19-9 was found before the intervention and the immunodetections performed on the operation part were positive for CEA and CA 19-9. The serous amounts of these markers were normalized after operation. To the author's knowledge, the interest of dosing the serous tumor markers in the observation of such a type of tumor is not mentioned in the literature. The recurrences are frequent and sometimes late even when the initial excision has been macroscopically satisfactory. A new increase of the serous amount of the markers could allow for an earlier detection of a recurrence during the patient follow-up. At present, the prognosis of these malignant forms remains very poor as the 5-year survival does not exceed 25%.