Surgery, by definition, is a challenge to the hemostatic system. In addition, a surgical procedure may provoke inappropriate venous or arterial thrombosis, such as is suggested historically by Virchow’s Triad. For these reasons, proper functioning of the hematologic system is integral in a successful and safe perioperative period. Patients with a disorder of either coagulation or hemostasis, therefore, present an exciting challenge to the preoperative physician. Diagnosis of a hematologic disorder may be more or less occult. A proper bleeding and clotting history can serve to elucidate such a disorder and is therefore paramount to the preoperative workup. For those patients with a previously diagnosed disorder of the hematologic system, appropriate laboratory investigation and a concise therapeutic plan for the day of surgery can help to minimize risks in the perioperative period.