Warfarin is the most common oral anticoagulant used for chronic anticoagulation therapy. Even without any antecedent trauma overanticoagulation can result in intracranial hemorrhage. The triad of anticoagulation with warfarin, age greater than 65 years, and traumatic head injury frequently produces a lethal brain hemorrhage. A retrospective review of more than 2000 patients admitted to the Trauma Service between September 1998 and May 2000 produced 278 patients with head injury and CT-documented intracranial hemorrhage. Of these patients 21 were admitted with an elevated prothrombin time (PT) due to anticoagulation with warfarin. Eighteen patients (86%) were above the age of 70. The most common indications for anticoagulation were atrial fibrillation (71%), deep venous thrombosis (19%), aortic valve replacement (9%), and ischemic cerebral infarcts (9%). Fourteen injuries were the result of a fall, one resulted from a gunshot wound, and one resulted from an assault. The remaining five patients were excluded as their history, workup, and evaluation by neurosurgery suggested a spontaneous bleed leading to fall rather than a fall causing a traumatic bleed. The average Glasgow Coma Score on admission was 11. The average PT and International Normalized Ratio (INR) on admission were 19.2 and 2.99 respectively. Eight of the 16 patients analyzed died. The risk of intracranial hemorrhage with relatively minor head injury is increased dramatically in the anticoagulated patient. A mortality rate of 50 per cent far exceeds the mortality rate in patients with similar head injuries who are not anticoagulated. In addition the risk/benefit equation of anticoagulation for the elderly is more complex and differs from that for younger patients. Perhaps more frequent and judicious monitoring of prothrombin time levels with lower therapeutic ranges (INR 1.5-2) is necessary.