The Framingham Study has been in operation since January 1949. Originally a direct field study of the NHLI it is now a cooperative activity of the NHLI and the Boston University Medical Center. The original design called for an investigation of the natural history of coronary heart disease and hypertension in a population of 5,127 adult men and women. As the study progressed other atherosclerotic and hypertensive diseases were also included. Particular attention was paid to the various manifestations of cerebrovascular disease. Beginning in 1971 a detailed study of all subjects manifesting or suspected of having demonstrated symptoms or signs of cerebrovascular disease has been carried out. This study will continue for another two years. It is anticipated that the number of subjects developing this disorder will become sufficiently high that assessment of risk factors for stroke and the natural history of this disorder can be definitively determined. The Stroke Study involves the clinical evaluation of all living subjects remaining in the Framingham cohort and the review of all information concerning death, hospitalization or other evidence of illness which has occurred in this population. Initial examination by a clinic physician is followed by a careful neurologic appraisal in those persons in whom any suspicion of cerebrovascular disease has been raised. Reviews of all ancillary information pertaining to the health status of the subjects are conducted by a committee of several well-qualified physicians.