Severely obese patients undergoing surgery carry a higher risk for pulmonary thromboembolism than normal weight patients, with a potentially fatal outcome. We present a case of pulmonary thromboembolism occurring after mandibular reconstruction surgery in a severely obese patient. A 48-year-old man (180 cm, 142.4 kg, BMI 43.95 kg/m2) presented with left-side mandibular gingival cancer and underwent mandibular reconstruction with an anterolateral thigh flap and fibular flap. Although heparin was administered for 5 days after the operation, the patient developed a pulmonary thromboembolism 7 days after the operation. Heparin administration was re-started, and the thrombus disappeared within 3 weeks after onset. The patient exhibited good morphological and functional results at 1-year follow-up. In the present case, intraoperative and postoperative management was performed in accordance with the guidelines, but pulmonary thromboembolism nevertheless occurred. Extreme caution must be used when operating on severely obese patients.
