V.N. Krasnozhen, E.M. Pokrovskaya 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 Kazan City Hospital No. 16. We performed endoscopic cystectomy using a microdebrider in 98 patients with maxillary sinus cysts and 10 patients with sphenoid sinus cysts. All surgeries utilized an ElePs instrument set, endoscopes, and microdebrider. Following submucosal injection of a local anesthetic, a special trocar was used to perforate the anterior wall of the maxillary sinus. Upon entering the sinus cavity, the trocar was removed, leaving a sleeve through which a 4 mm diameter endoscope with 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.