Endoscopic sinus surgery (ESS) is the most used surgical approach in the treatment of chronic and recurrent maxillary rhinosinusitis. However, it still remains unclear how well surgery restores the mucociliary function in damaged maxillary sinus mucosa. There is also controversy whether to enlargen the natural ostium or not. We examined the mucociliary clearance (MCC) of maxillary sinuses in 27 patients with chronic and recurrent rhinosinusitis. On one side only an uncinectomy was done, on the contralateral side a middle meatal antrostomy was additionally performed. The mucociliary clearance (MCC) was measured in both sides preoperatively and 9 months after the operation. Measurements of the mucociliary clearance in maxillary sinuses were done using an isotope method. Preoperative mean residual activity on the uncinectomy side was 87.2 % and postoperative mean residual activity 94.1 %. On the middle meatal antrostomy side mean preoperative residual activity was 92.3 % and postoperative mean residual activity 88.4 %. Residual activity was considered as good (< or = 50 %) on the uncinectomy side in 2 sinuses (7.4 %) preoperatively and in 1 sinus (3.7 %) postoperatively. On the middle meatal antrostomy side residual activity was considered good in 1 sinus (3.7 %) preoperatively and in 4 sinuses (14.8 %) postoperatively. Mucociliary function remained poor even 9 months postoperatively. Surgery did not significantly improve the mucociliary function of maxillary sinus mucosa in chronic or recurrent rhinosinusitis. There was no statistical difference between operative techniques. In this study it seemed however, that uncinectomy combined with the enlargening of the natural ostium may restore maxillary sinus mucociliary clearance (MCC) better than uncinectomy alone.