The popularity of the fibular free flap in mandibular reconstructions is persisting, and major donor area complications rarely occur after fibular free flap operations. Still, we have observed a pseudo–compartment syndrome in a 52-year-old patient on the 12th postoperative day after a mandibular reconstruction with a fibular free flap. When an obstruction in the deep venous system (deep vein thrombosis) was observed in the Doppler ultrasound-guided imaging, the patient has been taken to the operating room for an emergency surgery and the donor area has been completely reopened (in the manner of a fasciotomy). After this procedure, the circulation in the foot appeared to return to normal. The exposed muscles of the patient, who was started on a low-molecular-weight heparin treatment for the deep vein thrombosis, have been closed with skin grafts on the 10th day. No functional loss was observed during the 2-month follow-up period.