Orthognathic surgery including maxillary osteotomy, mandibular osteotomy, and genioplasty is a reliable treatment strategy for jaw deformity. However, there are some complications associated with these surgeries, including neurovascular damage and abnormal bleeding. The authors present here a patient of aspiration pneumonia after mandibular osteotomy.An 18-year-old female patient underwent sagittal split ramus osteotomy and genioplasty for mandibular prognathism. She began choking and coughing immediately after surgery. She was diagnosed with aspiration pneumonia based on chest radiography and computed tomography findings. Her hyoid bone was shifted 23 mm inferiorly after surgery, and this movement may have caused swallowing dysfunction. She was treated with intravenous antibiotics and discharged on the 18th postoperative day.Although the hyoid bone is transiently shifted inferiorly by mandibular setback with or without genioplasty, this shift does not usually affect swallowing function. Damage to the suprahyoid muscles during genioplasty may cause both an inferior shift and dysmobility of the hyoid bone. Therefore, surgeons must be careful not to damage the suprahyoid muscles at the lingual site osteotomy in genioplasty to avoid this complication.