Background: Identifying the cause of nasal obstruction is critical before surgical intervention. Structural nasal obstruction, due to nasal valve stenosis, is unlikely to benefit from simple septoplasty and turbinate reduction. This study assesses changes in nasal peak inspiratory flow (NPIF) as a tool for discriminating decongestable versus structural obstruction. Methodology: Cross-sectional study of patients undergoing nasal airflow assessment was performed. Rhinomanometry, nasal obstruction visual analogue scores (VAS) and NPIF were performed pre- and post-decongestion. Population groups were defined with decongestable or structural obstruction by relative post-decongestion changes in airways resistance and symptoms. Results: Fifty two patients were assessed, 24 with decongestable, 28 with structural obstruction. Pre- and post-decongestion NPIF were similar between groups. Absolute and percentage NPIF change were larger with decongestable versus structural obstruction. Sensitivity and specificity for predicting decongestable obstruction were 75.0% and 60.7% for NPIF increase >20 L/min; 75.0% and 64.3% for NPIF increase >20%. The respective positive predictive values were 62.1% and 64.3%. Conclusion: NPIF increase after decongestion is larger with decongestable than structural nasal obstruction. NPIF alone cannot discriminate the two conditions and does not replace more formal assessment.