Endoscopy is needed for reliable evaluation of the treatment of nasal polyposis. In this study, we compared the reproducibility of various score systems for staging nasal polyposis and the inter-individual variations between investigators. The mass of the polyps was assessed by five methods, three new techniques (numbers 1, 2 and 3) and two established ones (numbers 4 and 5). These were: 1, lateral imaging projecting the extension of the polyps by drawing on a schematic picture of the lateral wall of each nasal cavity; 2, assessment of polyp obstruction estimating the proportion of the total nasal cavity volume occupied by polyps; 3, nasal airway patency--determining the relationship between the patient's patent airway lumen and an imaginary maximal nasal airway lumen; 4, a score system with four steps ad modum Lildholdt et al.--determining their relationship to fixed anatomical landmarks; and 5, a score system with three steps ad modum Lund and Mackay--determining their relationship to the middle meatus. High correlations were found between the first and the second assessments by a given investigator with all five methods used to score nasal polyposis. High correlations were also shown between the various methods. When three investigators examined a given patient, there were no significant differences between the investigators using score systems 1, 3 and 4. However, with score systems 2 and 5, there was insufficient agreement between the investigators. The patient's symptom of nasal blockage was not a good indicator of the size of the polyps, especially as regards small polyps. Two of the best methods tested (1 and 4) were selected for further clinical studies regarding evaluation of the sensitivity of score systems to detect changes in polyp size during treatment.