It is believed that local factors within the nasal cavities contribute to the formation of nasal polyps. The disruption of local homeostasis mechanisms in a chronic inflammatory process is one of those factors. Cyclooxygenase (COX)-2 expression is activated in the course of the immune response to extracellular and intracellular stimuli. Also, an increase of the gene expression can be associated with the development of nasal polyps in patients with chronic sinusitis.The aim of this study was an evaluation of the role of the -765G/C COX-2 polymorphism in sinusitis pathogenesis in patients with nasal polyps.The study group consisted of 100 patients, aged 35–65, with chronic sinusitis and nasal polyps and 150 people in the age, sex-, age- and ethnicity-matched control group. The study material included DNA isolated from peripheral blood lymphocytes of the patients and the controls. PCR-RFLP method was used in genotyping polymorphic variants of COX-2.In comparison to the control group, the group of the patients with chronic sinusitis and nasal polyps showed a statistically significant increase in the occurrence frequency of the -765G/C polymorphic variant of COX-2 gene (OR 4.04; 95% CI 2.32–7.03; p > 0.001) and C allele (OR 3.68; 95% CI 2.38–5.68; p < 0.001).The -765G/C genotype of COX-2 can be associated with an increased risk of the occurrence of chronic sinusitis with nasal polyps in the Polish populationCOX-2, polimorfizm genów, stany zapalne nosa i zatok, polipy nosa