Nasal CPAP therapy has been found to be the most effective treatment of OSAS apart from tracheotomy. Its long-term application, however, can cause several ENT complications like dryness of the nasal and pharyngeal mucosa, rhinitis and an increased frequency of sinusitis and infections of the lower airways. CPAP therapy is not applicable if nasal resistance is elevated, so that septal correction may become necessary. Unsuccessful UPPP can cause pressure loss through the mouth during CPAP therapy and in this case tracheotomy remains the only alternative. In order to evaluate the clinical significance of flexible nasopharyngoscopy with Mueller's manoeuvre (FNMM), we compared the endoscopic findings of 71 patients with their individual CPAP pressure required to keep their pharynx patent during sleep, 22 patients showed poor pharyngeal wall movement, 23 patients had moderate obstruction (about 50 percent closure) and 26 patients had nearly complete or complete pharyngeal obstruction. We found that patients with poor pharyngeal mobility needed a significantly lower CPAP pressure (mean 9 mbar) than those with nearly complete pharyngeal obstruction during FNMM (mean 11 mbar). Mean CPAP pressure of patients with moderate obstruction was 10 mbar, but this group could not be separated statistically from the other groups, indicating a not exactly defined category. Rhinomanometry showed no differences in nasal resistance between all groups. There was neither a correlation between CPAP pressure and rhinomanometry, nor between CPAP pressure and BROCA Index or distance of palatal arcs.