Factor XII deficiency is a rare autosomal recessive health condition usually discovered incidentally during routine coagulation screening before surgery after investigating a prolongation of the activated partial thromboplastin time. This is a case of a 29-year-old man from Saudi Arabia who was selectively admitted to the surgical department to treat a perianal fistula and found incidentally prolonged activated partial thromboplastin time and factor XII deficiency. Examination of the skin revealed no bruising, petechiae, or ecchymosis. Systemic examination was normal. Laboratory examination showed an activated partial thromboplastin time > 160 s (normal between 27 and 38), which was repeated twice with low factor XII < 5.7% (73-121). Other factors and the work of hemostasis were within the normal range. Surgery was delayed at the request of the patient. One year later, the patient was admitted to the clinic after surgery without bleeding and did not require factor correction before or after surgery. However, treating factor XII-deficient patients specifically for preoperative preparation is challenging. Therefore, this rare case should be recorded and reported the same way as a number of previously rarely reported cases.