Stylomandibular fusion is a poorly documented and rare complication of maxillofacial surgical procedures. This case report describes a patient presenting with stylomandibular false ankylosis following mandibular reconstruction. A 59-year-old female patient underwent segmental mandibular resection and reconstruction for a defect resulting from ameloblastoma surgery using an iliac crest free flap. A styloid fracture was detected postoperatively, and the patient was managed conservatively. In the third postoperative year, the patient presented with marked limitation of oral gape. A diagnosis of stylomandibular false ankylosis was made, and the patient underwent an ostectomy of the aberrant bone, with improved mouth opening. The abnormal union between the styloid process and the mandible is a previously unreported complication in the use of iliac crest free flaps. This case report emphasizes the importance of being vigilant for stylomandibular false ankylosis, especially when there is a restriction of oral aperture postoperatively following reconstructive procedures involving bone flaps.