Identifying the site of obstruction and the pattern of airway change during sleep are the key points essential to guide surgical treatment decision making for Obstructive Sleep Apnoea-Hypopnoea Syndrome in adults. In this investigation, 250 cases were retrospectively analyzed in order to compare the pharyngolaryngeal endoscopic findings detected in the awake state, with those obtained in drug-induced sedation, by means of the Sleep Endoscopy technique. All endoscopic findings have been classified according to the semi-quantitative NOH staging. The awake and sedation NOH resulted identical in 25% of the cases only, while the discrepancies involved the oropharyngeal and hypopharyngeal sites, respectively in about 33% and 50% of the patients. The laryngeal obstructive role detected during sedation in almost 33% of the cases was both unforeseen and relevant, with all the consequent implications in the treatment choices particularly for the surgical cases.