Factor Ⅺ （FⅪ） deficiency indicates a decrease in FⅪ activity. It is a rare disease with an incidence of 1 in 1 million people in Japan. This disease is often asymptomatic, and spontaneous bleeding is rare, but it may be difficult to stop bleeding during trauma or surgery, so careful treatment planning and management are required.
A 69-year-old man with no previous history of difficulty in hemostasis presented to the outpatient department with a mandibular fracture. Open reduction and fixation of the mandible was scheduled, and a preoperative screening blood coagulation test revealed prolongation of the activated partial thromboplastin time （aPTT） （51.0 seconds）. Measurement of coagulation factor activity confirmed FⅪ deficiency （48％）. During the surgery, 4 units of FFP were administered, and the surgery was performed safely without any abnormal bleeding or difficulty in hemostasis. The postoperative course was uneventful, and the patient was discharged on the 9th postoperative day.