Objectives In clinical practice, lateral nasal wall collapse during forced inspiration is widely regarded as a sign of nasal obstruction or criterion indicating nasal valve surgery. This study aims to evaluate the relationship between the degree of lateral nasal wall collapse and subjective nasal obstruction. Design Case-Control study Setting Tertiary centre hospital Participants Case group consisted of 24 patients who had been diagnosed with a deviated nasal septum or nasal valve stenosis. Control group consisted of 27 volunteers with no nasal obstruction symptoms and no septal deviation on nasal endoscopy. Main outcome measures Lateral nasal wall collapse is determined by the degree of lateral nasal wall triangle (LNWT) area reduction on frontal view during forced inspiration compared to quiet inspiration. LNWT area ratio of the patient and control groups was compared. The relationship between the lateral nasal wall collapse and clinical factors including symptom scores, nasal valve angles, skin thickness were evaluated. Results The average LNWT area ratio of the patient (n=24) and control groups (n=27) was 0.96 and 0.83 respectively (p=0.001). Symptom score (NOSE and VAS) is not related to the degree of lateral nasal wall collapse. Moreover, nasal valve angle and skin thickness were also not related to the degree of lateral nasal wall collapse. In 14 of the 19 patients, the more obstructed side corresponded to the side of narrower nasal valve angle, and 5 were not. Conclusion Lateral nasal wall collapse is not related to a patients’ nasal obstruction.