This article describes a unique complication after chin bone harvesting. The complication consisted of fracture and posterior displacement of the lingual cortical plate that did not occur at the time of the operation but during the healing phase. The bone was harvested for a bilateral sinus lift procedure. Diagnosis was made by chance with the aid of a postoperative CT scan that was taken to study the sinus area. The mandibular scans revealed a bony fragment 2 to 4 mm in width and 3 cm in length fractured and displaced 1 cm posteriorly. This bony fragment was pedicled to the geniohyoid and genioglossus muscles. The patient was asymptomatic, and no treatment was carried out. The patient is still symptom-free 16 months after the initial diagnosis of the fracture.