Warfarin is a once-daily oral anticoagulant. It is used for the prophylaxis and treatment of a range of conditions with an increased thrombotic risk. Warfarin acts as an indirect vitamin K agonist via binding to vitamin K epoxide-reductase complex 1. This prevents conversion to active vitamin K, which is essential for hepatic synthesis of the coagulation factors II, VII, IX, and X. Anticoagulant effects occur within 24–72 hours, once the already synthesised Vitamin K dependent clotting factors are depleted. Drug monitoring, via the international normalised ratio, is crucial due to its narrow therapeutic window, other known drug interactions and genetic variations in cytochrome P450 enzyme expression. Warfarin reversal may be required in both the emergency and elective urological settings with the administration of reversal agents such as vitamin K and prothrombin complex concentrate.