Experimental studies suggest that bone marrow-derived endothelial progenitor cells (EPCs) play an important role in the maintenance of endothelial integrity and hemostasis. The number of circulating EPC has been shown to be inversely correlated with cardiovascular risk factors and vascular function and to predict cardiovascular events independent of both traditional and non-traditional risk factors. Thus, EPCs provide a clinical advantage over the use of other biomarkers as their measurement is directly associated with endothelial function, and available evidence suggests that they are consistently and significantly associated with a spectrum of cardiovascular complications, such as acute coronary syndromes and coronary artery disease. However, many issues in the field of EPC isolation and identification, particularly in regards to the effective and unequivocal molecular characterization of these cells still remain unresolved. In addition, simple EPC counts do not adequately describe cardiovascular disease risk. This limitation is attributable to variation in the definition of EPCs, the number of existing cardiovascular risk factors in different patients as well as a difference in the interaction between EPCs and other hematopoietic progenitor, inflammatory cells or platelets.