Objective: The purpose of this study was to correlate changes in PSG parameters between the diagnostic polysomnogram (dPSG) and the first night of treatment with continuous positive airway pressure (CPAP) (cpapPSG) to subjective improvement in sleep quality.Background: In patients with obstructive sleep apnea syndrome (OSAS), therapy with CPAP results in reduction of sleep latency, stage 1 sleep, arousal index (Al) and respiratory disturbance index (RDI), and increase in stage 2 sleep, REM sleep and REM density. No data exists on the differences in polysomnographic (PSG) parameters in patients who have subjective improvement in sleep quality and those who do not.Methods: We retrospectively reviewed PSG studies of 44 patients with OSAS who presented to the Sleep Disorders Center at Duke University Medical Center. Patient's qualitative assessment of sleep was noted using a Likert-type scale administered the morning after the dPSG and cpapPSG. PSG indices of patients noting subjective improvement were compared to those with no improvement.Results: Patients noting a subjective improvement in sleep quality showed a decrease in the percentages of stage 1 sleep (P<0.001) and an increase in percentages of stages 3 and 4 sleep (slow wave sleep rebound; P<0.007) and stage REM sleep (REM rebound; P<0.008).