Stroke is the third leading cause of death in the United States after heart disease and cancer; it has an incidence of approximately 750,000 cases per year, and it is a leading cause of disability in adults. The factors predicting a poor outcome from stroke include severe initial neurological dysfunction, hypertension, cardiac arrhythmias, myocardial infarction, hypercholesterolemia, and diabetes mellitus. The armamentarium available for improvement of neurological function after stroke is currently limited to placement in specialized stroke units, optimal therapy for medical complications, and intense physical, occupational and speech rehabilitation. Despite many trials, no pharmacological intervention has been shown convincingly to improve neurological outcome. This review was undertaken to determine the appropriate time for new approaches to the therapy of stroke such as the infusion of stem cells into the central nervous system. The literature shows in large case series that functional recovery from stroke reaches a maximum level by 3-6 months after onset, and no further recovery occurs beyond this time. Nevertheless, about 80% of these patients reach their maximum function for activities of daily living within 6 weeks from onset. Initiation of a clinical trial of stem cell therapy would require demonstration of optimal clinical improvement by neurological evaluations, with no change over at least 4 weeks of observation. Accordingly, in subjects with first-ever ischemic stroke who remained neurologically unchanged from the second until the third month after the acute event, implementation of stem cell therapy would be appropriate at approximately 3 months after the stroke.