Ameloblastic fibrosarcoma is a malignant odontogenic tumor that rarely affects the skull base and surrounding regions. We present a case of a 48-year-old man with histologically confirmed malignant transformation of a benign ameloblastic fibroma 10 years after initial presentation of a localized facial mass. The ameloblastic fibrosarcoma extended from the facial region to the orbit, anterior and middle fossa skull base, the infratemporal fossa, and the cavernous sinus. Progressive proptosis with complete monocular vision loss was the presenting symptom. To our review, our case represents the first report of intradural extension of ameloblastic fibrosarcoma. Using a multidisciplinary skull base approach, resection of all tumors except that in the cavernous sinus was achieved with the resulting defect reconstructed with an anterolateral thigh free flap. The patient had no new neurologic deficits after surgery and underwent adjuvant fractionated radiation therapy. Malignant transformation of ameloblastic fibroma into ameloblastic fibrosarcoma can occur many years after initial presentation. Thus, vigilant long-term follow-up is essential despite the benign nature of the initial pathologic lesion. Use of a multidisciplinary approach is critical in obtaining the optimal outcome in these complex cases.