Rationale Chronic rhinosinusitis is characterized by persistent inflammation of the nasal and paranasal mucosa with numerous emigrated leukocytes. L-selectin on leukocytes and its endothelial glycosylated ligands initiate organ-specific leukocyte infiltration into inflamed tissues. Objectives The purpose of this study was to evaluate the endothelial expression of functionally active endothelial L-selectin ligands, sulfated sialyl Lewis x, in maxillary sinus mucosa from patients with chronic rhinosinusitis or normal controls. Methods 116 maxillary sinus mucosa specimens were obtained surgically and immunohistochemically stained with monoclonal antibodies detecting sialyl Lewis x or sulphated extended core 1 lactosamines. The severity of the inflammation was determined by intraoperative endoscopic findings, the computed tomography scans, and the histopathological assessment of the specimens. Measurements and Main Results The percentage of vessels expressing endothelial sulfated sialyl Lewis x epitopes increased during chronic rhinosinusitis compared to uninflamed control tissue, especially in patients with additional allergic rhinitis, and decreased in specimens from aspirin intolerant patients with preoperative oral corticosteroid treatment. In addition, the expression level of endothelial sulfated sialyl Lewis x epitopes and the number of mucosal eosinophils correlated with the severity of the inflammation; and decreased in 9 months postoperatively taken specimens compared to the intraoperative ones, especially in patients with intranasal corticosteroid treatment. Conclusions Our results suggest that functionally active L-selectin ligands might guide leukocyte traffic into maxillary sinus mucosa preferentially in patients with severe findings of chronic maxillary rhinosinusitis, thus leading to the aggravation of the inflammation.