INTRODUCTION: Chronic rhinosinusitis (CRS) is a common disease, but yet little is known about its pathogenesis, including the role of respiratory viruses. OBJECTIVES: To correlate the presence of respiratory viruses and CRS. MATERIALS: A prospective cross-sectional study to identify genomes of respiratory viruses in patients with CRS with polyps (CRSwNP) and without polyps (CRSsNP) by real-time PCR. Maxillary and nasal washes, middle turbinate mucosa, maxillary sinus mucosa and nasal polyps were analyzed. Eosinophils, neutrophils and lymphocytes was quantified, and tomographic scores were calculated according to Lund-Mackay. RESULTS: 132 patients were evaluated (31 controls, 31 CRSsNP and 70 CRSwNP). 35% control patients, 53% patients with CRSwNP and 45% patients with CRSsNP, had positive samples. Human metapneumovirus and human rhinovirus were the most frequently detected virus. The seasonality pattern found in CRS patients matches with periods of viral circulation in patients with acute respiratory illness. In CRSsNP the virus presence was associated to a lower count of lymphocytes and neutrophils. In CRSwNP group, the virus presence was associated to a higher count of lymphocytes and neutrophils and to a lower count of eosinophils. No difference was found on Tomographic scores. CONCLUSIONS: Respiratory viruses were detected in a high proportion in CRS. The seasonal pattern found rejects the hypothesis of viral persistence and reinforces the possibility that these patients have asymptomatic infections and acts as "reservoirs" in periods of low virus circulation. The changes in cellularity pattern suggests that respiratory viruses may affect CRS inflammatory course, even not influencing the disease extension.