OBJECTIVE The aim of this study was to ascertain the most reliable objective measurement for the assessment of nasal patency by investigating the relationship between peak nasal inspiratory flow, peak oral inspiratory flow, and the nasal patency index in relation to the patient's subjective perception regarding nasal obstruction. METHODS Prospective cohort study. METHODS This study included 131 volunteers of both genders, aged 18 years or older, with or without nasal symptoms, who were able to give informed consent, completed the study protocol, and could speak and write Dutch fluently. Peak nasal inspiratory flow and peak oral inspiratory flow were performed and nasal patency index was computed. The results were evaluated and compared with the subjective perception of nasal passage, using the validated Nasal Obstruction Symptom Evaluation scale and visual analog scale for nasal passage. RESULTS Our study showed that peak nasal inspiratory flow, nasal patency index and nasal patency visual analog scale correlate with the Nasal Obstruction Symptom Evaluation scale in contrast to peak oral inspiratory flow. Peak nasal inspiratory flow and nasal patency index also showed significant association with the Nasal Obstruction Symptom Evaluation scale after adjustment for confounders. CONCLUSIONS Peak nasal inspiratory flow is the most reliable method for the assessment of nasal patency. It is quick, inexpensive, and easy to perform, and correlates significantly with the subjective feeling of nasal obstruction. There is no clinical need to measure peak oral inspiratory flow or to calculate the nasal patency index in the evaluation of nasal patency. METHODS 4