Background: Nasal polyposis (NP) is a multifactorial pathology with negative impact on quality of life. The pathogenesis of NP has not been fully elucidated. This limits the pathogenic treatment. Recent studies suggest that nitric oxide (NO) and its metabolites are involved in pathophysiological events of NP. Purpose of the study: to evaluate the tissue NO and nitrite/nitrate (NO2 -/NO3 -) levels in patients with and without NP and to establish the relationship between NO levels and some clinical features. Material and methods: 86 recruited patients were divided into a case group (N1=43), patients with NP and a control group (N2=43), patients with septal deviations and turbinate hypertrophies. Visual Analog Scale (VAS) was used to evaluate the severity of nasal obstruction and olfactory disturbances. NO and NO2 -+NO3 - concentrations in tissue specimens were measured by spectrometric method. Results: Case group had significantly lower NO (U=173.5, p<0.001) and NO2 -+NO3 - levels (U=123.5, p<0.001). A negative correlation was found between VAS for nasal obstruction and NO levels (rs = -0.379, p<0.05), between VAS for olfactory disturbances and NO levels (rs = -0.531, p<0.001), and between endoscopic score and NO levels (rs = -0.758, p<0.05). Conclusions: Our results corroborate the previous findings. This underlines that NO levels depend on the patency of sinus ostium and the state of osteomeatal complex. Further studies, which take into account the role of NO in different rhinosinusitis endotypes, are needed to be performed in order to improve the NP management.