Background: Chronic rhinosinusitis (CRS) 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 leukocyte infiltration into inflamed tissues. Endoscopic sinus surgery (ESS) is the major approach for restoring sinus physiology after failure of conservative therapy; however, the effect of enlarging the maxillary sinus ostium is still unknown. Here, we compared two histological markers of local inflammation, the number of mucosal eosinophils, and the expression of endothelial L-selectin ligands, with clinical outcomes after enlarging or saving the maxillary sinus ostium.Methods: Twenty-three patients with CRS underwent uncinectomy on one side and additional middle meatal antrostomy on the other side. Maxillary sinus mucosa biopsy specimens from these patients and nine healthy subjects were taken for immunohistochemical evaluations of the number of mucosal eosinophils and endothelial L-Selectin ligands. Also, symptoms and mucociliary clearance were measured.Results: The postoperative reduction of the endothelial L-Selectin ligands was independent of the operation technique. There was a correlation between postoperative number of mucosal eosinophils and symptom score, which was also independent of the surgical technique. The postoperative decrease of mucosal eosinophils, as well as the correlation of the intraoperative eosinophils with the postoperative symptom score, was found only on antrostomy side.Conclusion: ESS decreases the expression of endothelial L-Selectin ligands, which might lead to decreased eosinophil traffic into maxillary sinus mucosa, putatively more when enlarging the maxillary sinus ostium. Both intra- and postoperative low number of eosinophils seem to be indicators of good subjective recovery.