Autologous endothelial progenitor cell (EPC) populations represent a novel treatment for therapeutic revascularization and vascular repair for diabetic patients with complications including diabetic retinopathy. Current therapies are applicable to late-stage disease and carry significant side effects, whereas cell-based therapy may provide an alternative by repairing areas of vasodegeneration and reversing ischemia. However, EPCs from diabetic patients with vascular complications are dysfunctional. Moreover, the diabetic environment poses its own challenges and complicates the use of autologous EPCs. Before EPCs become the ideal “cell therapy,” the optimal EPC must be determined, any functional dysfunction must be corrected prior to use, and the diabetic milieu will require modification to accept the EPCs. This review describes the rationale for harnessing the vascular reparative properties of EPCs with emphasis on the molecular and phenotypic nature of healthy EPCs, how diabetes alters them, and novel strategies to improve dysfunctional EPCs.