The objective of the present study was to evaluate the effectiveness of the treatment of the children presenting with acute purulent rhinosinusitis based on the concentration of lactoferrin in the serum. Material and methods. The study involved 298 children suffering from acute purulent rhinosinusitis. The patients were divided into two groups depending on the mode of treatment. Those comprising the control group (n=166) were treated in compliance with the standard scheme that included antibacterial therapy and (according to indications for endonasal drainage of the maxillary sinuses) the insertion of catheters, the use of the displacement technique as described by Proetto, the physiotherapeutic treatment of the nose, and the application of the vasoconstrictor nasal drops. The patients of the study group (n=132) were given the treatment according to the conventional scheme with the additional prescription of a topical corticosteroid agent (mometasone furoate). Results. The evaluation of the results of the treatment was carried out based on the subjective sensations of the children and/or their parents at discharge from the hospital and within one month after the termination of the treatment by making use of the visual analogue scale for pain (in scores). The concentration of lactoferrin in the serum was determined before and after the treatment. Initially, all the patients had the increased level of acute phase protein lactoferrin compared with the physiological norm. The patients of the main group experienced a three-fold (on the average) decrease in the serum lactoferrin level at discharge reaching the physiological norm, it continued to decrease during one month after the treatment. In the control group, the level of lactoferrin recovered more slowly compared with that in the patients of the study group which suggests the lack of effectiveness of the treatment. The concentration of lactoferrin (in the main group) was normalized under the action of the nasonex spray which gave evidence of the strong anti-inflammatory effect of the combined treatment. The study has demonstrated the statistically significant difference between the two groups at discharge from the hospital and one month after the completion of the treatment (t=1,96, p=0,06). Conclusion. It can be concluded that dynamics of the serum lactoferrin level is an important criterion for the effectiveness of the treatment of the children presenting with acute purulent rhinosinusitis.