Objective To review the biological behaviour of endothelial progenitor cells and their role in vascular diseases. Data sources The data used in this review were mainly from Medline and PubMed for relevant English language articles published from 1985 to March 2007. The search term was "endothelial progenitor cells". Study selection Articles about the biological behaviour of endothelial progenitor cells and their roles in the pathogenesis of vascular diseases such as atherogenesis were used. Results Progenitor cells in bone marrow, peripheral blood and adventitia can differentiate into mature endothelial cells (ECs). The progenitor cells, which express certain surface markers including AC133, CD34 and KDR, enable restoration of the microcirculation and ECs when injury or ischaemia occurs. Endothelial progenitor cells used in experimental models and clinical trials for ischaemic syndromes could restore endothelial integrity and inhibit neointima development. Moreover, their number and functional properties are influenced by certain cytokines and atherosclerotic risk factors. Impairment of the progenitor cells might limit the regenerative capacity, even lead to the development of atherosclerosis or other vascular diseases. Conclusions Endothelial progenitor cells have a particular role in prevention and treatment of certain cardiovascular diseases. However, many challenges remain in understanding differentiation of endothelial progenitor cells, their mobilization and revascularization.