Carcinoma ex pleomorphic adenoma (CEPA) is a rare, aggressive, poorly understood malignancy. In CEPA, an epithelial malignancy develops in association with a primary or recurrent benign pleomorphic adenoma. Carcinoma ex pleomorphic adenoma is very difficult to identify before surgery because the clinical presentation of many cases is similar to that of pleomorphic adenomas. The risk for malignancy increases with the duration of a mixed tumor. Treatment of CEPA must be individualized on the basis of the tumor location, involvement of adjacent structures, histologic subtype, and grade. The authors recently experienced a case of CEPA arising in the oral cavity with neck metastasis. The patient was a 70-year-old man presenting a huge mass that was present for 20 years and that slowly grew on the left side of the neck. We treated it with a total excision with wide margins and neck dissection. There was no recurrence during the follow-up period of 5 years up until now. We present a case of an unusually huge CEPA in the oral cavity.