Objective—To evaluate whether changes in concentrations of circulating adhesion molecules are related to disease activity in patients with giant cell arteritis (GCA). Methods—A sandwich ELISA was used to measure soluble intercellular adhesion molecule-1 (sICAM-1), sICAM-3, vascular cell adhesion molecule-1 (sVCAM-1), E-selectin (sE-selectin), and L-selectin (sL-selectin) in serum and plasma samples from patients with GCA. A cross sectional study was performed on 64 GCA patients at diVerent activity stages and on 35 age and sex matched healthy donors. Thirteen of these patients were evaluated at the time of diagnosis and serially during follow up. Results—At the time of diagnosis, sICAM-1 concentrations were significantly higher in active GCA patients than in controls (mean (SD) 360.55 (129.78) ng/ml versus 243.25 (47.43) ng/ml, p<0.001). In contrast, sICAM-3, sVCAM-1, sE-selectin, and sL-selectin values did not diVer from those obtained in normal donors. With corticosteroid administration, a decrease in sICAM-1 concentrations was observed, reaching normal values when clinical remission was achieved (263.18 (92.7) ng/ml globally, 293.59 (108.39) ng/ml in the group of patients in recent remission, and 236.83 (70.02) ng/ml in those in long term remission). In the 13 patients followed up longitudinally, sICAM-1 values also normalised with clinical remission (225.87 (64.25) ng/ml in patients in recent remission, and 256.29 (75.15) ng/ml in those in long term remission). Conclusions—Circulating sICAM-1 concentrations clearly correlate with clinically apparent disease activity in GCA patients. DiVerences with results previously found in patients with other vasculitides may indicate that diVerent pathogenic mechanisms contribute to vascular inflammation in diVerent disorders