Objectives: Nasal endoscopy is a cornerstone in diagnosing sinonasal disease, but different raters might generate different results using the technique. Our study aims to evaluate the agreement between multiple raters to assess the validity of nasal endoscopy. Design/Participants: Three independent and blinded raters evaluated 28 patients (56 nasal cavities) diagnosed with chronic rhinosinusitis according to the European Position Paper on Rhinosinusitis and Nasal Polyps. The ratings were compared using unweighted Fleiss' kappa coefficients (Kf) for each objective parameter. Setting: The department of Otorhinolaryngology, Odense University Hospital, Denmark. Main outcome measures: The ratings were quantified in a modified Lund-Kennedy endoscopy score and focused on the objective parameters specified in the diagnostic criteria: polyps, oedema and discharge. Results: The raters agreed on the findings concerning polyps and discharge but not regarding oedema with the inter-rater agreement for the different parameters being: polyps Kf=.66 (SE .07, P<.001), oedema Kf=.05 (SE .07, P=.21), discharge Kf=.35 (SE .08, P<.001), oedema exclusively in middle meatus Kf=-.07 (SE .04, P=.8) and discharge exclusively in middle meatus Kf=.16 (SE .07, P=.01). Conclusion: Using nasal endoscopy, the evaluation of polyps by multiple raters showed sufficient reliability indicating an acceptable objective evaluation. The evaluation of discharge achieved a fair level of agreement while the assessment of oedema could not achieve a sufficient reliability questioning the inclusion of oedema in the criteria for diagnosing sinonasal disease.