A.A. Blotsky, M.Yu. Tseplyaev, N.V. Kalinichenko, L.N. Manakova, O.N. Deniskin, Amur State Medical Academy, Blagoveshchensk. The treatment of chronic sinusitis remains a pressing issue. Despite conservative and surgical treatments, chronic sinusitis tends to be protracted and recur multiple times. Over the past decade, there has been a steady increase in chronic sinusitis, despite the use of state-of-the-art medications for its treatment. Depending on the nature of the pathomorphological process localized in the maxillary sinuses, otolaryngologists perform various types of surgical interventions. As a rule, for proliferative forms of chronic sinusitis, extranasal opening of the maxillary sinuses is used, which is not without its drawbacks. The introduction of microendoscopic technology into modern rhinology has expanded the scope of organ-preserving interventions in the maxillary sinus. This makes it possible to perform functional surgery while preserving the sinus's bony structures and mucosa. However, insufficient visual control and the inconvenience of manipulation within the sinus cavity limit the indications for these interventions and, in some cases, lead to unsatisfactory postoperative outcomes. The aim of this study was to develop an effective method for the removal of localized proliferative processes in the maxillary sinus. To remove localized proliferative lesions localized in the maxillary sinus cavity (cysts, isolated polyps) identified by cranial magnetic resonance imaging, we used endoscopic maxillary sinusotomy, using an endoscopic system with 0°, 30°, and 90° endoscopes and a standard set of instruments. We also used contact laser interstitial thermotherapy of proliferative mucosal lesions using a high-energy ATKUS-15 semiconductor laser in 21 patients. Preoperatively, all patients underwent magnetic resonance imaging to determine proliferative processes in the maxillary sinus. Axial and sagittal projections were particularly valuable for determining the location and size of pathological lesions. Surgeries were performed under both local and general anesthesia. After perforating the facial wall of the maxillary sinus with a trocar and inspecting its cavity, a laser light guide was advanced through a channel parallel to the endoscope and directed toward the proliferative lesion under video control. If necessary, an additional opening was created adjacent to the first trocar to allow for the light guide to be inserted. The laser was applied in a contact, continuous mode, using the distal end of the light guide at a power of 8 W. If the natural ostium of the maxillary sinus was compromised, its patency was restored. The procedure was completed with loose nasal packing. The patient was discharged from the hospital 5-7 days after the procedure. We observed no complications following these procedures. Thus, the use of high-energy laser irradiation in microendoscopic interventions on the maxillary sinuses made it possible to preserve almost the entire functionally active mucous membrane and bone structures of the sinus, expand the indications for these surgical interventions, increase their effectiveness, and prevent the development of relapses of the disease.