Nasal and oral corticosteroid therapy is the ultimate treatment for sinonasal polyposis. Although there are numerous clinical studies regarding the factors associated with the formation of nasal polyposis, there is not enough literature on how these factors are influenced by steroid treatment. Twenty-one patients that had no prior medical therapy for nasal polyposis or had received medical therapy at least 6 months earlier were included in the study. Patients were treated with oral and nasal corticosteroid therapy. Nasal polyp biopsies were taken before and after medical treatment and immunohistochemical staining for cyclooxygenase 2 (COX-2), vascular endothelial growth factor (VEGF) and inducible nitric oxide synthase (iNOS) were applied to the specimens. In this study, we tried to demonstrate the effects of corticosteroid therapy on nasal polyposis tissue immunohistochemically. There was no change at immunohistochemical expression level of COX-2; however, the decline of immunohistochemical expression levels of VEGF and iNOS was statistically significant. Short-term steroid therapy does not affect COX-2 level of the nasal polyposis tissue, but has an influence on iNOS and VEGF levels. Our findings were harmonious with those of the previous studies of the literature. Further studies are needed to demonstrate the long-term effects with a larger patient group.