Introduction. Chronic rhinosinusitis with polyps and asthma are comorbid, mutually aggravating, and difficult to treat diseases. The correlation between the severity of chronic rhinosinusitis with polyps and eosinophilic asthma, the similarity of the endotypes of these diseases and the success of humanized monoclonal antibodies for the treatment of severe asthma explain the interest in studying the possibility of using this group of drugs in patients with chronic rhinosinusitis with polyps. Aim. The aim of the study was to assess changes in the severity of symptoms of chronic rhinosinusitis in patients with comorbid asthma against the background of reslizumab treatment. We evaluated clinical effect of treatment, dynamics of subjective and objective characteristics of symptoms of chronic rhinosinusitis and asthma, indices of total and local eosinophilia. Material and methods. The study involved 18 patients with severe eosinophilic asthma selected for treatment with reslizumab. Study protocol: The first examination, performed before starting reslizumab treatment, included assessment of clinical symptoms using the standardized Sino-nasal Outcome Test-22 (SNOT-22) and Asthma Control Test (ACT) questionnaires, endoscopic nasal cavity examination, spiral computed tomography of the paranasal sinuses, rhino cytogram, determination of eosinophils and eosinophilic cationic protein (ECP) in blood, allergological examination using ImmunoCAP method, and external respiratory function study. The results of treatment were evaluated after 6 injections of reslizumab at the dose of 3 mg/kg weight once every 4 weeks. The obtained data were processed using Statistica 12.0 program (StatSoft, USA). The differences were considered statistically significant at p<0,05. Results and discussion. When assessing the outcomes of treatment after 6 injections of reslizumab, both a marked improvement in asthma control (Asthma Control Test – increase from 7,0 [6–8] to 22,0 [16–22]) and a decrease in nasal symptoms (SNOT-22 was 78,0 [62–81] and 39,0 [29–49], respectively) were noted. There was a significant improvement in the Lund-Mackay spiral computed tomography data of the paranasal sinuses (16,0 [11–19] and 7,0 [5–12], respectively), spirometry values, and a decrease in eosinophils and eosinophilic cationic protein content in the blood. In the presence of polyposis rhinosinusitis in patients with severe eosinophilic asthma, a more pronounced effect of reslizumab on the attenuation of asthma symptoms was obtained comparing to patients without polyps. Conclusions. Treatment with reslizumab in patients with eosinophilic asthma and concomitant chronic rhinosinusitis with polyps and eosinophilic chronic rhinosinusitis leads not only to better control of asthma symptoms but also to a significant regression of nasal symptoms.