Background and Purpose-In aged humans, stroke is a major cause of disability for which no neuroprotective measures are available. Granulocyte-colony stimulating factor (G-CSF), a member of the cytokine family of growth factors, promotes brain neurogenesis and improves functional outcome after stroke in young animals. We tested the hypothesis that G-CSF provides a restorative therapeutic benefit in aged animals. Methods-Focal cerebral ischemia was produced by reversible occlusion of the right middle cerebral artery in 19-to 20-month-old male Sprague-Dawley rats. One hour after reperfusion, the aged rats were treated daily with 15 g/kg G-CSF and for 15 days total. Rats were behaviorally tested and the brains removed for analysis at 28 days poststroke. Results-G-CSF treatment after stroke exerted a robust and sustained beneficial effect on survival rate and running function. Transient improvement after G-CSF treatment could be observed for coordinative motor function on the inclined plane test and for working memory in the radial-arm maze test. At the cellular level, G-CSF treatment increased the number of proliferating cells in the subventricular zone and dentate gyrus and also increased the number of newborn neurons in the subventricular zone ipsilateral to the lesion. Conclusions-These results suggest that G-CSF treatment in aged rats has a survival-enhancing capacity and a beneficial effect on functional outcome, most likely through supportive cellular processes such as neurogenesis.