The objective of the present study was to estimate the effectiveness of the long-term treatment with low doses of macrolides for the prevention of early relapses of polypous rhinosinusitis in the postoperative period. A total of 66 patients at the age from 18 to 77 years presenting with the clinical diagnosis of bilateral polypous rhinosinusitis were randomly allocated to 3 groups; fifty five patients completed the study. All the patients underwent endoscopic polysinusotomy. All of them were given basal therapy with mometasone furoate at a daily dose of 400 mcg throughout 6 month postoperative period. The patients of groups 1 (n=22) and 2 (n=14) additionally received daily doses of 25 mg clarithromycin during 6 and 3 months respectively. The patients of group 3 were given basal therapy alone. All the patients were followed up within 6, 12, and 24 weeks after surgery with the use of a visual-analog scale, SNOT-20 questionnaire, acoustic rhinometry and rhinomanometry, endoscopic study of the nasal cavity, computed tomography of paranasal sinuses, determination of saccharine transport time, evaluation of olfactorial sense, and measurement of the eosinophilic cationic protein level in the nasal secretion. It was demonstrated that the patients treated with clarithromycin show significantly better outcomes of therapy compared with controls (p<0.05), the effectiveness of the 6 month clarithromycin therapy being higher than that of the 3 month treatment. The exception was the results of estimation of clinical symptoms and signs based on the visual-analog scale and the acoustic rhinometric data that did not reveal significant differences between the groups. The patients of the control group given no clarithromycin significantly more frequently developed relapses of polypous rhinosinusitis (p=0.02).