The most widely reported surgical procedure for obstructive sleep apnea syndrome is uvulopalatopharyngoplasty. The success rate for this procedure is variable, and the reason for failure is incompletely understood. Failure in some patients is postulated to result from tongue-base obstruction. To investigate this, we identified the level of collapse and obstruction in 11 cases of uvulopalatopharyngoplasty failure, using upper airway manometry and videoendoscopy, while patients slept. Airway manometry measured the initial level of complete obstruction. Videoendoscopy identified significant resting airway narrowing (> 75%) at the tongue base on obstructed compared with nonobstructed breaths. Results of manometry indicated that the palate was the primary level of obstruction in eight (73%) compared with the tongue base in three (27%). However, collapse on videoendoscopy at the tongue base was observed in an additional three patients. A total of six patients (54%) demonstrated significant tongue-base abnormalities. In six patients with uvulopalatopharyngoplasty as the only pharyngeal surgery, one (17%) has an obstruction at the tongue base, as measured with manometry. Three of the six also had collapses at the tongue base, as measured endoscopically. Tongue-based abnormalities were identified in four of six (67%). Two additional patients who had failed uvulopalatopharyngoplasty and transpalatal advancement pharyngoplasty had obstructions on manometry at the level of tongue base. Six of eight (75%) palatopharyngoplasty failures demonstrated tongue-base collapse. In the three patients with tongue-base surgery, all had obstructions on manometry at the palate and none had endoscopic tongue-base collapse. These results indicate that in most uvulopalatopharyngoplasty failures the initial level of obstruction occurs at the palate.(ABSTRACT TRUNCATED AT 250 WORDS)