Uvulopalatopharyngoplasty (UPPP) was performed in 12 patients with obstructive sleep apnea. Pre-surgical clinical and polysomnographic data were compared with those one to three months after surgery. Excessive daytime sleepiness was partially improved in 4 cases and completely abolished in 8. Total sleep time, sleep efficiency, number of arousals and sleep latency were similar in both evaluations. REM latency to stage 2 markedly increased on the follow-up. Stage distributions were similar in both nights except for stage 4 which was more frequently absent on the first recording. Sa02 levels below 80% were seen in 10 cases before UPPP and in 4 after it. Apnea index decreased in all cases but it reached normal levels only in 4.