The trial was sponsored by the National Center, Lung, and Bloodstream Institute . Extra support was provided by Abbott Laboratories, which had no role in the reporting or conduct of the trial. An executive committee fulfilled weekly and monitored the daily conduct of the trial. An independent basic safety and data monitoring committee was appointed by the NHLBI. The Duke Clinical Analysis Institute coordinated all aspects of global trial operations, site management and monitoring, data collection, statistical analyses, and reporting.Passman, M.D., M.S.C.E., Vincenzo Di Lazzaro, M.D., Richard A. Bernstein, M.D., Ph.D., Carlos A. Morillo, M.D., Marilyn Mollman Rymer, M.D., Vincent Thijs, M.D., Ph.D., Tyson Rogers, M.S., Frank Beckers, Ph.D., Kate Lindborg, Ph.D., and Johannes Brachmann, M.D. For the CRYSTAL AF Investigators: Cryptogenic Stroke and Underlying Atrial Fibrillation Ischemic stroke is probably the leading causes of death and disability.1 The reason remains to be unexplained after routine evaluation in 20 to 40 percent of cases, resulting in the classification, by exclusion, of cryptogenic stroke.2-6 Atrial fibrillation is a well-recognized cause of ischemic stroke,7 though the risk is reduced by anticoagulation7,8 Documentation of atrial fibrillation is required to initiate anticoagulant therapy after ischemic stroke.8 In the lack of documented atrial fibrillation, antiplatelet brokers are recommended.7 Provided the paroxysmal and asymptomatic nature of atrial fibrillation often, it could not be detected with the use of traditional monitoring techniques.9-12 Strategies for detection of atrial fibrillation have included in-hospital monitoring,13 serial electrocardiography ,14,15 Holter monitoring,16 monitoring by using exterior event or loop recorders,17-22 long-term outpatient monitoring,23-28 and monitoring through insertable cardiac monitors ,29-31 yielding recognition rates ranging from 0 to 25 percent.