An excessively anticoagulated 52-year-old man on chronic warfarin therapy developed a forearm compartment syndrome after venipuncture in an antecubital vein. At fasciotomy, active venous bleeding into the forearm from the venipuncture site was noted, and a large forearm hematoma was evacuated. Anticoagulated patients or those with coagulopathies are at risk for compartment syndrome after percutaneous needle punctures and should be warned of this possibility. Such individuals should be instructed to seek immediate medical attention if any signs or symptoms of this complication occur.