Between July 1, 1961, and June 30, 1965, 4,748 patients with signs and symptoms of ischemic cerebrovascular disease were admitted to various institutions for prospective investigation. The mean age for the group was 60 years. Two thirds were below 65 years of age. A significantly larger proportion of nonwhites were in the age group below 55. Eighty-four percent were white, and men outnumbered women 2:1. Interinstitutional differences in clinical status of patients were noted, particularly between vascular surgical and neurologic services. Complete arteriographic studies showing intracranial and extracranial circulation were accomplished in 80%. Twenty-five percent of the patients had no lesions demonstrated or had surgically inaccessible lesions only. The remainder had surgically accessible lesions, both with or without inaccessible lesions. A higher proportion of patients with surgically accessible lesions was noted among whites.