C hroniC subdural hematoma (cSDH) is a disease of the elderly and demonstrates an incidence of approximately 3.4 patients per 100,000 persons younger than 65 years of age and 8 to 58 patients per 100,000 persons older than 65 years. 1,4,9 The prevalence of cSDH is expected to rise as the percentage of the United States population older than 65 years grows from 12% in 2003 to a projected 20% by 2030. 17Other identified risk factors for the development of cSDH include male sex, history of falls, chronic alcohol use, and antiplatelet or anticoagulant therapy, with warfarin increasing the relative risk of developing cSDH by aBBreViatiONS ADP = adenosine diphosphate; ASA = acetylsalicylic acid; AT = antithrombosis; CAD = coronary artery disease; cSDH = chronic subdural hematoma; DVT = deep venous thrombosis; INR = international normalized ratio; LMWH = low-molecular-weight heparin; TIA = transient ischemic attack. OBJectiVe Antithrombosis (AT), defined here as either antiplatelets or anticoagulants, is a significant risk factor for the development of chronic subdural hematomas (cSDHs). Resuming AT following the evacuation of cSDH is a highly variable practice, with scant evidence in the literature for guidance. Here, a retrospective analysis of a cohort of patients from a single institution undergoing surgical drainage of cSDH was performed to evaluate postoperative complications and determine the optimal timing of the resumption of common antithrombotic agents. methOdS This retrospective analysis was performed on 479 patients undergoing surgical evacuation of cSDH at St. Michael's Hospital over a 5-year period (2007)(2008)(2009)(2010)(2011)(2012). The collected variables included the type of AT agent, indications for AT, timing and type of postoperative complications, and the restart intervals for the AT agents, when available. Postoperative complications were classified as major hemorrhages, minor hemorrhages, or thromboembolic events. reSultS Among all 479 study patients, 71 experienced major hemorrhage (14.8%), 110 experienced minor hemorrhage (23.0%), and 8 experienced thromboembolism (1.67%) postoperatively. Patients on any type of preoperative AT regimen were at a higher risk of major hemorrhage (19.0% vs 10.9%; OR 1.93; 95% CI 1.15-2.71; p = 0.014). The type of AT agent did not affect the frequency of any postoperative complications. Patients on any preoperative AT regimen experienced earlier postoperative major hemorrhages (mean 16.2 vs 26.5 days; p = 0.052) and thromboembolic events (mean 2.7 vs 51.5 days; p = 0.036) than those patients without a history of AT; the type of AT agent did not affect timing of complications. Patients who were restarted on any AT therapy postoperatively were at decreased risk of major rebleeding following resumption than those patients who were not restarted (OR 0.06; 95% CI 0.02-0.2; p < 0.01). cONcluSiONS Patients with a history of preoperative AT experienced thromboembolic complications significantly earlier than those patients without AT, which peaked at 3 days postoperative...