Medical institution: Kazan State Medical Academy. Objective: to develop the most optimal minimally invasive endoscopic techniques for treating cysts of the maxillary and sphenoid sinuses. Materials and methods. Clinical studies were conducted at the ENT department of the 16th city hospital of Kazan. We performed endoscopic cystectomy using a microdebrider in 98 patients with cysts of the maxillary sinuses and 10 patients with cysts of the sphenoid sinuses. All surgeries were performed using a set of instruments, endoscopes, and a microdebrider from ElePs. After injecting a local anesthetic under the mucous membrane, the anterior wall of the maxillary sinus was perforated using a special trocar. Upon penetration into the sinus cavity, the trocar was removed, leaving a sleeve through which an endoscope with a diameter of 4 mm and a viewing angle of 0° and 70° was inserted. The cyst was removed using a microdebrider inserted into the trocar sleeve. The sphenoid sinus was accessed through the superior nasal meatus. Under the guidance of a 2.7 mm endoscope, the sphenoid sinus ostium was identified and dilated if necessary. Cystectomy was performed using a microdebrider inserted into the lumen of the sphenoid sinus through the trocar sleeve. Results. This technique is optimal for cysts located on the inferior wall of the maxillary sinus. In all patients, reactive effects from the soft tissues of the cheek were minimal in the postoperative period. The patient's hospital stay was 2-3 days. During dynamic observation of patients, 2 cases of cyst recurrence were noted, which occurred after 1 year. Conclusion. The technique we used is effective and safe. Its advantage over traditional surgeries is a shorter surgical time and minor local reactive effects in the postoperative period. This makes it possible to reduce the length of hospital stay for patients. V.N. Krasnozhen, E.M. Pokrovskaya