Factor XII deficiency is an important hematological problem which is characterized by isolated prolongation of the activated partial thromboplastin time and presents with thrombosis and thromboembolism tendency rather than expected bleeding diathesis in clinical practice. A 55-year-old male patient who was scheduled for aortic coronary bypass graft surgery had elevated activated partial thromboplastin time (109.4 sec) as a laboratory finding. The patient was diagnosed with factor XII deficiency and operated in our clinic. No thromboembolic event was seen during follow-up. The patient was discharged in the seventh postoperative day uneventfully. Herein, we highlight the importance of this disease due to its rare occurrence and present our treatment strategy applied.