To cite this article: Hastan D, Fokkens WJ, Bachert C, Newson RB, Bislimovska J, Bockelbrink A, Bousquet PJ, Brozek G, Bruno A, Dahlén SE, Forsberg B, Gunnbjörnsdóttir M, Kasper L, Krämer U, Kowalski ML, Lange B, Lundbäck B, Salagean E, Todo-Bom A, Tomassen P, Toskala E, van Drunen CM, Bousquet J, Zuberbier T, Jarvis D, Burney P. Chronic rhinosinusitis in Europe - an underestimated disease. A GA(2) LEN study. Allergy 2011; 66: 1216-1223. ABSTRACT: Background: Chronic rhinosinusitis (CRS) is a common health problem, with significant medical costs and impact on general health. Even so, prevalence figures for Europe are unavailable. In this study, conducted by the GA(2) LEN network of excellence, the European Position Paper on Rhinosinusitis and nasal Polyps (EP(3) OS) diagnostic criteria are applied to estimate variation in the prevalence of Chronic rhinosinusitis (CRS) for Europe. Method: A postal questionnaire was sent to a random sample of adults aged 15-75 years in 19 centres in Europe. Participants reported symptoms of CRS, and doctor diagnosed CRS, allergic rhinitis, age, gender and smoking history. Definition of CRS was based on the EP(3) OS diagnostic criteria: the presence of more than two of the symptoms: (i) nasal blockage, (ii) nasal discharge, (iii) facial pain/pressure or (iv) reduction in sense of smell, for >12 weeks in the past year - with at least one symptom being nasal blockage or discharge. Results: Information was obtained from 57 128 responders living in 19 centres in 12 countries. The overall prevalence of CRS by EP(3) OS criteria was 10.9% (range 6.9-27.1). CRS was more common in smokers than in nonsmokers (OR 1.7: 95% CI 1.6-1.9). The prevalence of self-reported physician-diagnosed CRS within centres was highly correlated with the prevalence of EP(3) OS-diagnosed CRS. Conclusion: This is the first European international multicentre prevalence study of CRS. In this multicentre survey of adults in Europe, about one in ten participants had CRS with marked geographical variation. Smoking was associated with having CRS in all parts of Europe.