The National Institute of Neurological and Communicative Disorders and Stroke initiated the Stroke Data Bank, which is a multicenter project to prospectively collect data on the clinical course and sequelae of stroke. Additional objectives were to provide information that would enable a standard diagnostic clinical evaluation, to identify prognostic factors, and to provide planning data for future studies. A brief description of the structure and methods precede the baseline characterization of 1,805 patients enrolled in the Stroke Data Bank between July 1983 and June 1986. Two thirds of these patients were admitted within 24 hours after stroke onset. Medical history, neurologic history, and hospitalization summaries are presented separately for the following stroke subtypes: infarction, unknown cause; embolism from cardiac source; infarction due to atherosclerosis; lacune; parenchymatous or intracerebral hemorrhage; subarachnoid hemorrhage; and other. The utility and limitations of these data are discussed.