Subclinical atherosclerosis has been demonstrated in patients with early rheumatoid arthritis (ERA) without any signs of cardiovascular disease (CVD). The aim of this study was to investigate the relationship between serum YKL-40 level and arterial stiffness in patients with ERA. Forty two patients with ERA and 35 healthy controls with no history or current sign of CVD were included in the study. ERA patients with active disease, defined as DAS28 a parts per thousand yen3.2, and symptoms onset < 12 months were recruited. Arterial stiffness was evaluated by carotid-femoral pulse wave velocity (CF-PWV), and the intima-media thickness carotid (IMT-C) was measured by carotid ultrasonography. Serum YKL-40 levels were measured by an enzyme-linked immunoassay method. The mean age was 43.1 +/- A 5.8 years in ERA patients and 41.0 +/- A 5.9 years in control group. The CF-PWV and IMT-C of the ERA patients were determined significantly higher than the control group (P = .001, P < .001, respectively). YKL-40 levels were significantly elevated in ERA patients than controls (P = .008). The serum levels of YKL-40 in the ERA patients showed a strong correlation with CF-PWV (r = .711, P < .001) and IMT-C (r = .733, P < .001). Multiple linear regression analysis revealed that CF-PWV could be explained by serum YKL-40 levels (adjusted RA(2)A = .493, P < .001). We have shown that patients with ERA had increased CF-PWV and serum YKL-40 levels. In addition, there was an association between CF-PWV values and serum YKL-40 levels in patients with ERA. As a result, we believe that serum YKL-40 level and CF-PWV might reflect early atherosclerosis in patients with ERA.