Alterations in pharyngeal structure and function are considered fundamental in the pathogenesis of obstructive sleep apnea (OSA). However, little is known about morphologic features of the pharynx in patients with OSA. We therefore studied the tissue composition of the uvula (midsagittal section) in patients with OSA, using a quantitative, morphometric point-counting technique. Uvula tissue was obtained by uvulopalatopharyngoplasty (UPPP) in 33 patients (mean number of apneas per hour of sleep = 32.7 +/- 5.2) and by autopsy in 22 normal subjects not known to have OSA. All statistical comparisons were controlled for differences caused by age and body mass index. Patients with OSA had a significantly greater percentage of muscle in the uvula (18.1 +/- 1.9% versus 9.3 +/- 2.1%, p = 0.02) than did normal subjects. A significant difference in fat content was also found (9.5 +/- 1.4% in patients versus 4.0 +/- 1.0% in normal subjects, p less than 0.02). These differences between patients with OSA and control subjects could not be accounted for by anthropometric or sex differences. The percentage of uvula fat tissue was significantly related to the frequency of apneas and hypopneas in sleep (r = 0.43, p less than 0.01). Uvula morphology in 6 nonapneic snorers undergoing UPPP was similar to that of patients with OSA. We conclude that the uvula in patients with OSA contains more muscle and fat than the uvula in control subjects, possibly contributing to pharyngeal narrowing in OSA.