Objective— Estradiol (E ₂ ) is known to accelerate reendothelialization and thus prevent intimal thickening and in-stent restenosis after angioplasty. Transplantation experiments with ERα ^−/− mice have previously shown that E ₂ acts through local and bone marrow cell compartments to enhance endothelial healing. However, the downstream mechanisms induced by E ₂ to mediate endothelial repair are still poorly understood. Methods and Results— We show here that after endovascular carotid artery injury, E ₂ -enhanced endothelial repair is lost in osteopontin-deficient mice (OPN ^−/− ). Transplantation of OPN ^−/− bone marrow into wild-type lethally irradiated mice, and vice versa, suggested that osteopontin plays a crucial role in both the local and the bone marrow actions of E ₂ . In the vascular compartment, using transgenic mice expressing doxycyclin regulatable-osteopontin, we show that endothelial cell specific osteopontin overexpression mimics E ₂ -enhanced endothelial cell migration and proliferation in the regenerating endothelium. In the bone marrow cell compartment, we demonstrate that E ₂ enhances bone marrow–derived mononuclear cell adhesion to regenerating endothelium in vivo, and that this effect is dependent on osteopontin. Conclusions— We demonstrate here that E ₂ acceleration of the endothelial repair requires osteopontin, both for bone marrow–derived cell recruitment and for endothelial cell migration and proliferation.