This study aimed to investigate the effect of chronic rhinosinusitis/nasal polyposis on the severity of COPD and to find out whether the 'united airway disease' hypothesis is valid for COPD. The study enrolled 90 patients diagnosed and staged according to criteria of an international guideline for diagnosis and management of COPD. The patients in stages I and II were classified as Group 1 and the patients in stages III and IV as Group 2. All the patients were questioned about the presence of major and minor criteria of sinusitis, underwent paranasal sinus computed tomography (PNS-CT) scans, and answered a questionnaire based on a quality of life test for sinusitis (SNOT-20). Sinusitis was present in 48 (53%) patients according to criteria of major and minor symptoms, and in 58 (64%) patients according to Lund-Mackay scoring system of PNS-CT. There was no significant difference in CT score between Group 1 and Group 2 (2.3 +/- 0.5 vs. 2.1 +/- 0.4, p > 0.05). However, the frequency of minor symptoms was greater in Group 2. SNOT-20 score was significantly higher in Group 2 than in Group 1 (28.7 +/- 1.7 and 22.2 +/- 1.9, respectively, p = 0.014). A significant correlation was determined between Lund-Mackay and SNOT-20 scores. The presence of CRS should be assessed in COPD patients, especially in those with severe disease. Further research is needed to disclose possible common immunopathological mechanisms in the pathogeneses of COPD and CRS.