Background: Rheumatoid arthritis (RA) is associated with increased morbidity and mortality attributable to accelerated atherosclerosis and cardiovascular events. Objective: To determine the role played by endothelial progenitor cells (EPC) in the defence system against arteriosclerosis. Methods: The number and function of EPC in 13 young patients with RA with low disease activity (DAS28 3.5 (0.3)) and 13 healthy control subjects was studied. Endothelial function was investigated by agonist-induced, endothelium dependent vasodilatation measured by the forearm blood flow technique. Migratory activity and adhesion of EPC to tumour necrosis factor α (TNFα) activated mature endothelial cells and components of the extracellular matrix were tested in vitro. Putative precursor populations (CD34⁺, CD34 ⁺/CD133⁺, and CD34⁺/KDR⁺ haematopoietic stem cells) were measured by flow cytometric analysis. Results: Acetylcholine-induced, endothelium dependent vasodilatation was reduced by about 50% in patients with RA, indicating endothelial dysfunction, whereas endothelium-independent vasodilatation in response to glyceryl trinitrate was at control level. Significantly reduced numbers of EPC were found in the patients compared with controls. Migratory activity of EPC was decreased in patients with RA. Adhesion to mature endothelial cells after activation with TNFα was enhanced only in controls. The adhesion to matrix proteins and the number of putative precursor cell lineages was comparable in both groups. Conclusion: Endothelial dysfunction in patients with RA with low grade inflammation is associated with a reduced number and partial dysfunction of EPC. Further studies are needed to explore whether interventions that potentially ameliorate the number and function of EPC also improve endothelial function in these patients.