We conducted a prospective study of 50 adults to investigate changes in nasal mucociliary clearance following endoscopic intranasal dacryocystorhinostomy (DCR). Each operation was performed with the use of a drill to perforate the lateral nasal wall in order to reach the lacrimal sac. Each patient's mucociliary clearance time (MCT) was determined by the saccharin test on both the operated and nonoperated sides; the preoperative times were compared with postoperative measurements made 1 and 3 months following DCR. Preoperatively, the mean MCTs were 14.48 minutes on the operated side and 14.50 minutes on the nonoperated side-not a statistically significant difference (p > 0.05). Postoperatively, the corresponding MCTs were 25.22 and 14.98 minutes at 1 month and 18.44 and 15.62 minutes at 3 months. On the operated side, both postoperative MCTs were significantly longer than the preoperative value (p < 0.001), while on the nonoperated side, neither postoperative MCT was significantly different from the preoperative value (p > 0.05). Also, the postoperative MCTs were significantly longer on the operated side than on the nonoperated side at both 1 month (p < 0.001) and 3 months (p < 0.05). Only 1 of the 50 operations was considered to be unsuccessful; the reason for this surgical failure was the patient's ongoing complaints of chronic postoperative dacryocystitis. We conclude that endoscopic DCR disturbs mucociliary clearance. Changes in MCTs may be attributable to injury to the nasal mucosa or to the continuous flow of tears through the nasal mucosa.