V. M. Isaev, V. G. Zenger, A. N. Nasedkin, Z. M. Ashurov, A. V. Reshetnikov Moscow Regional Research Clinical Institute named after M. F. Vladimirsky Moscow Medical Academy named after I. M. Sechenov Rada-Pharma LLC Inflammatory diseases of the nose and paranasal sinuses remain the most common ENT diseases. Among them, the most common is damage to the maxillary sinus. The problem of treating purulent sinusitis remains relevant, despite certain successes in the use of modern antibiotics, taking into account the sensitivity of flora to them, and a variety of gentle surgical methods for this pathology. The antitumor activity of photodynamic therapy (PDT) is well known. In addition, there is evidence of the use of PDT in the complex treatment of purulent wounds and trophic ulcers due to its bactericidal action and influence on the production of cytokines and cell growth factors. We have developed a new treatment for acute and chronic purulent sinusitis. This method is based on the antibacterial effect of PDT on the purulent process. In this case, the effect occurs as a result of a photochemical reaction caused by exposure of a photosensitizer injected into the inflammation site to laser radiation with a wavelength matching the photosensitizer's absorption peak. The method was used to treat purulent sinusitis in 35 patients (19 men, 16 women) of working age. Two patients had bilateral purulent sinusitis, and one woman had a long-standing history of purulent polypous sinusitis. For PDT, the domestically produced photosensitizer "Radochlorin" with an absorption peak at 662 nm (manufactured by Rada-Pharma LLC, Moscow) was used. The MILON LAHTA diode laser device (registration certificate 29/01050603/5828, developed by Milon-Laser LLC) was used as the laser source. Patients underwent a comprehensive examination, including X-ray, CT, and, if necessary, endoscopic examination (maxillary sinusoscopy) to rule out cancer, foreign bodies, and other potential causes. All patients underwent a maxillary sinus puncture before the PDT session, the resulting fluid was collected for bacteriological testing, and antibiotic sensitivity was determined. A similar examination was performed 3-5 days and one month after the PDT session, which was performed once for all patients. It should be noted that during the PDT session, laser radiation was transmitted into the sinus via a quartz-polymer monofilament passed through the puncture needle. To facilitate permanent evacuation of sinus contents, a subclavian catheter was inserted for 3-5 days. Analysis of the results of PDT treatment for purulent sinusitis revealed that 33 of 35 patients, or 94%, achieved complete recovery (absence of complaints and clinical signs of the disease, with negative results from two bacteriological tests). PDT was ineffective in a man with odontogenic sinusitis and a woman with the polypous-purulent form of this disease. However, both these patients and the woman reported a significant improvement in their condition after the PDT session, and bacteriological testing showed an increase in the initially identified pathogen causing the purulent process in the sinus. We believe that the ineffectiveness of PDT in these two patients was associated with the persistence of cause-and-effect relationships in the development of odontogenic sinusitis and with technical difficulties in the polypous-purulent form, when polyps in the sinus prevented laser irradiation of the mucous membrane in full, which contributed to the preservation of pathogenic flora.