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Abstract Background Internal valve collapse is a frequent cause of nasal obstruction but remains poorly understood and is sometimes treated inappropriately as a result. No functional or imaging test for the condition has been validated and the reference diagnostic technique is physical examination. The objective of this study was to evaluate the potential of four‐phase rhinomanometry as a diagnostic test for internal valve collapse. Methods In a case–control diagnostic accuracy study, the nostrils of adult patients consulting for chronic nasal obstruction were classified as “collapsed” or “non‐collapsed” based on clinical findings. Four‐phase rhinomanometry was performed in all patients. The area defined by the path of the flow/pressure curve in the two phases of inspiration (the “inspiratory loop area” or “hysteresis loop area”) was calculated for both nasal cavities and the threshold value with the highest Youden index was identified. Results Sixty‐six patients (132 nostrils) were included with 72 nostrils classified as collapsed and 60 as non‐collapsed. Before nasal decongestion, the inspiratory loop area with the highest Youden index was 17.3 Pa L s−1 and the corresponding sensitivity and specificity were 88.3% (95% confidence interval, 80.0–95.0%) and 89.9% (82.6–95.7%), respectively. Conclusions In these patients, a cutoff inspiratory loop area in four‐phase rhinomanometry data reproduced clinical diagnoses of internal valve collapse with high sensitivity and specificity. This method may offer a firmer basis for treatment indications than subjective physical examinations. Level of evidence Level 4.