Introduction. Chronic atelectasis of the maxillary sinus, also known as «silent» sinus syndrome, is a condition characterized by hypoplasia of the maxillary sinus without symptoms of sinusitis enophthalmos, and facial asymmetry. It is suggested that the only effective treatment is endonasal endoscopic sinusotomy. To date, there is no convincing data in the literature about the effect of surgery on the restoration of the volume of the affected sinus and there is no generally accepted method for assessing the outcome of treatment. Aim of the study was to objectively assess the change in the absolute and relative volume of the maxillary sinus in children with chronic maxillary atelectasis (CMA) after endoscopic sinusotomy. Materials and methods. There are 17 children aged 6 to 15 years under prospective observation, who, according to the results of multispiral computed tomography, have been diagnosed with CMA. All patients underwent endoscopic endonasal sinusotomy. Evaluation of the treatment results was performed using the Volume Viewer program on the AW VolumeShare 7 graphic station of the Discovery CT750 HD apparatus by measuring sinus volume before and after surgical treatment. For objectification, we dynamically calculated the coefficient of the ratio of the sinus volume on the affected side and on the opposite side during observation periods of 6 months to a year. Results. After surgery, the airiness of the maxillary sinus in patients is restored; there is a significant increase in sinus volume in absolute values relative to the opposite side. Conclusions. The suggested authors’ method of objective control of sinus volume makes it possible to reliably evaluate the results of surgical treatment of the «silent» sinus and proves the effectiveness of a timely performed sinusotomy in relation to the correct development of the child’s facial skeleton.