The surgical correction of nasal obstruction is definitely effective and recommended in patients with poor CPAP compliance, often secondary to the high pressures that need to be given in patients with nasal sub stenosis. For this reason, the objective of this study is the evaluation of the effectiveness and effects of the functional nose surgery on adherence to CPAP- therapy in patients (with moderate to severe OSAS with indication of ventilation therapy) poorly compliant with CPAP. The study was performed on a sample of 52 patients, 40 male and 12 female, aged between 29 and 72 years followed by the Otolaryngology Unit of the University Palermo in the period between January 2015 and January 2017. All patients were subjected to the following s iter: anamnesis with Epworth Sleepiness Scale, NOSE scale, evaluation of “CPAP usage data.” Upper airway optical fiber endoscopy with Müller’s maneuver. We performed various type of nasal surgery (septoplasty, decongestion of the lower turbinates and FESS) 6 months after the surgery, CPAP usage was evaluated and the NOSE scale has been reapplied. All patients had a subjective degree of obstruction classified in severe or extreme by the NOSE scale before surgery. Almost all patients reported a mild degree of obstruction after the surgery. About CPAP usage, the average usage has passed by 2, 3 h at night to 6, 8 h after the surgery. The result is significant because it shows how the nasal functional surgery can make selected patients suitable to ventilation therapy. As our work shows, a better nasal function allows to reduce the CPAP pressure, Therefore, we believe that all patients with medium to severe obstructive apnea syndrome and for whom night-time ventilation therapy (CPAP) is advised should be evaluated with endoscopy and anamnesis oriented to evaluate nasal obstructive pathologies that may reduce effectiveness of CPAP.