Four university centers collaborated to contribute 1158 patients with acute episodes of cerebrovascular disease to the pilot Stroke Data Bank, initiated by NINCDS in 1978. During the pilot project a standard set of data collection forms were developed and used at each of the collaborating centers. Data on clinical course, laboratory findings, therapy and outcome were gathered prospectively throughout the patient's hospitalization and at specified follow-up intervals. Using operational definitions of stroke sub-types, consecutive cases were systematically allocated to specific categories of brain and vascular pathology. The definitions were based on clinical criteria as well as on laboratory data, including computerized tomography (CT), and angiography findings. This paper describes the pilot Stroke Data Bank and presents the distribution of cases by diagnostic and demographic categories. It represents one of the largest series of prospectively collected stroke cases studied by CT (90% of the cases) and angiography (42%). Based upon the methods and processes of this pilot study, a main phase of the Stroke Data Bank has been established to address a number of questions pertaining to stroke classification, evolution, diagnosis, and prognosis.