To examine endothelial function in rheumatoid arthritis patients and to assess whether clinical or genetic factors affect the development of endothelial dysfunction.Fifty-five patients fulfilling the 1987 American College of Rheumatology classification criteria for rheumatoid arthritis were recruited from Hospital Xeral-Calde, Lugo, Spain. Patients were required to have been treated for at least 5 years, including current treatment with one or more disease-modifying antirheumatic drugs. Patients with diabetes mellitus, renal insufficiency, or cardiovascular disease were excluded. Thirty-one age-, sex-, and ethnically matched controls were also studied. Endothelium-dependent (postischemia) and -independent (postnitroglycerin) vasodilatation were measured by brachial ultrasonography. Patients were genotyped for human leukocyte antigen (HLA)-DRB1.Patients had decreased endothelium-dependent vasodilatation (mean [+/- SD], 3.8% +/- 4.9%) compared with controls (8.0% +/- 4.5%; P <0.001). There were no differences in endothelium-independent vasodilatation. Clinical features were not associated with endothelial dysfunction. Endothelium-dependent vasodilatation was lower in the 30 rheumatoid arthritis patients with the HLA-DRB1*04 shared epitope alleles (2.4% +/- 4.1%) than in the remaining patients (5.5% +/- 5.3%; P = 0.01). Similar results were seen for patients with the HLA-DRB1*0404 shared epitope allele (-0.4% +/- 2.5%) compared with other patients (4.4% +/- 4.9%; P = 0.01).Patients with chronically treated rheumatoid arthritis had evidence of endothelial dysfunction, especially those with certain HLA-DRB1 genotypes. If confirmed, our results suggest that HLA-DRB1 status may be a predictor of cardiovascular risk in these patients.