Twenty-five adults with a deviated nasal septum, who complained about excessive daytime sleepiness, chronic fatigue, and nocturnal insomnia, were studied for one to two nights in a sleep laboratory. Recordings disclosed disordered breathing during sleep in the form of pronounced periodic breathing of alternating hypopneas and hyperpneas, isolated hypopneic episodes and central apneas and periodic sighs, all combined with electrophysiologic "microarousals," and a mixture of alpha and delta EEG wave activities. Surgical treatment of the deviated septum in 14 patients resulted in a subjective improvement in the level of diurnal alertness and in the quality of nocturnal sleep in 12 patients. Follow-up sleep recordings in seven of the patients who reported subjective improvement in sleep disclosed notably less waking and abnormal breathing during sleep. These results suggest that increased upper airway resistance can cause nonapneic breathing disorders in sleep and, consequently, sleep disturbances.