The aim of the present study is to elucidate the correlation between etiology and histology in nasal polyps with special regard to cystic fibrosis (CF). Nasal polyps from 15 children with CF and a control group of non-CF polyps from 15 adult patients were examined by light-microscopy. The histological evaluation was carried out on a blind basis in order to avoid bias. Among the parameters used, the tissue eosinophilia proved to be the most valuable factor in the differentiation between CF and non-CF polyps, as only few eosinophils were found in the CF-polyps. The polyp glands were few and generally pathological. Some characteristics abnormalities in the grandular morphology are apparently more common in CF polyps. It is concluded, that the histological examination of nasal polyps is of importance for the correct classification of the patient, but the diagnosis of CF cannot be made based on microscopy of polyps. Further studies including blinded histological examination of nasal polypous tissue might contribute to a more differentiated diagnose of nasal polyposis.