Polymyalgia rheumatica (PMR) is a common disorder of the elderly: the pathogenesis of the syndrome is still debated, though active synovitis of the shoulder has recently been confirmed. To investigate the pathogenesis of this synovitis we evaluated cell adhesion molecule (CAM) expression in shoulder synovial tissue from patients with PMR, correlated synovial expression with the serum levels of soluble forms, and assessed the changes associated with corticosteroid treatment. Arthroscopic synovial biopsies were obtained from 12 untreated and seven corticosteroid (CS)-treated cases. CAM expression was evaluated by MoAb staining on frozen sections and computerized image analysis. Soluble CAM were quantified by ELISA. Endothelial cells expressed intercellular adhesion molecule-1 (ICAM-1), E- and P-selectins. Infiltrating cells were ICAM-1 and beta1-integrin-positive, while L-selectin expression was limited to intravascular leucocytes. Synovial lining cells strongly expressed vascular cell adhesion molecule-1 (VCAM-1), and less intensely ICAM-1. Only the soluble form of ICAM-1 (sICAM-1) was elevated in untreated patients. CS treatment was associated with a decrease in ICAM-1, VCAM-1 and E- and P-selectin expression. sICAM-1 levels were in the normal range in treated patients. VLA-5 and 6 expression was widely distributed among cell types, and was not CS-sensitive. Active shoulder synovitis is associated with different CAM expression in PMR. ICAM-1 expression is widely distributed and correlates with elevated levels of the soluble form; it is significantly lower in CS-treated asymptomatic cases.