Deep venous thrombosis (DVT) is caused by obstruction of blood flow of the deep vein of the leg and accelerated blood coagulating activity. DVT may occur after an operation. However, there are few reports of DVT associated with surgery of the oral and maxillofacial region, especially in young adults.<BR>We report a case of DVT occurring after orthognathic surgery in a 19-year-old woman at our hospital. She had facial asymmetry and underwent Le Fort I osteotomy of the maxilla combined with sagittal splitting ramus osteotomy and intraoral vertical ramus osteotomy of the mandible under general anesthesia. Although she was able to walk the next day, symptoms of DVT appeared 3 days after the operation. On the 18th day after the first operation, surgery to remove the thrombus was performed by cardiovascular surgeons. She was discharged on the 34th day after the first operation.<BR>Orthognathic surgery is not free of the risk of DVT, which can cause fatal acute pulmonary thromboembolism. Therefore, it is necessary to prevent DVT after orthognathic surgery, even in young adults.