Increasing evidence points to a role for circulating endothelial progenitors, including populations of CD34-positive (CD34(+)) cells present in peripheral blood, in vascular homeostasis and neovascularization. In this report, circulating CD34(+) cells in individuals with a history of cerebral infarction were correlated with changes in neurologic function over a period of 1 year. Patients with decreased levels of CD34(+) cells displayed significant worsening in neurologic function, evaluated by the Barthel Index and Clinical Dementia Rating. These results support the hypothesis that levels of circulating CD34(+) cells have prognostic value for neural function, consistent with their potential role in maintaining cerebral circulation.