OBJECTIVE: To evaluate the impact of different types of nasal septum deformity (NSD) on nasal obstruction, rhinitis severity and response to medical treatment among pediatric persistent allergic rhinitis (PER) patients. METHODS: In a prospective, real-life study, 150 children and adolescents (mean age 13 ± 2.8 years, females 32.6%) diagnosed with PER according to ARIA guidelines were assessed by nasal endoscopy for NSD according to Mladina's classification, their response to medical treatment (intranasal steroids and antihistamines or antileucotriens), the presence of comorbidities, rhinitis severity (modified-ARIA criterion) and nasal obstruction visual analog scale score (VAS). RESULTS: Most patients (87%) had 1 of the 7 types of septal deformities. There was a high prevalence of bilateral (types 4 and 6; 46%) and anterior unilateral (types 1 and 2; 25%) NSD in patients not responding to medical treatment. Type 4 (OR = 6.4; p = 0.005) or type 6 (OR = 4.4; p = 0.03) NSD increased the risk of lack of improvement with medical treatment. Coexistence of anterior unilateral or bilateral NSD with severe turbinate enlargement increased >20-fold the risk of lack of improvement. Patients with bilateral NSD presented greater rhinitis severity. Non-responder adolescents displayed higher prevalence of bilateral NSD than children (53% vs. 23%; p = 0.02). Nasal obstruction VAS was higher for patients with anterior than posterior NSD, and greater for patients with bilateral NSD than any other type of septal morphology. CONCLUSION: Nasal endoscopy shows that bilateral and unilateral anterior nasal septum deformities are strongly associated with a poor response to medical treatment, greater rhinitis severity and higher nasal obstruction VAS. Consequently, nasal endoscopy is necessary in the PER patients to understand the disease severity as well as to plan a specific surgical treatment in order to improve nasal obstruction, disease severity, and patient's quality of life.