With the knowledge that anticoagulant drugs were effective in significantly reducing the incidence of cerebral embolic phenomena1,2and the evidence that in animals anticoagulants might increase the severity of experimental hemorrhagic infarcts,3-5the study of cerebral embolic phenomena in man has taken on new importance. This paper examines three aspects of cerebral embolism in man—the usual clinical course, the prognostic signs of significance, and the effects of anticoagulation upon the clinical outcome. I. The Natural History The present study is an effort to delineate the clinical features and course of cerebral embolic phenomena. In previous pathological studies6,7the natural history of those episodes ending in death has been considered, but this hardly gives a verisimilitude of the usual clinical course. The records of 185 patients with a diagnosis of cerebral embolism admitted to the New York Hospital over the past 18 years were critically assayed. In 82