Respiratory events (RE) during sleep induce cortical arousals (A) and marked changes in autonomic markers in sleep apnea syndrome (SAS). The aims of the study were double. First, we assessed whether pulse wave amplitude (PWA) added to polysomnography (PSG) could improve RE and A detection; second, we wanted to know whether the quality of detection of these two parameters could be improved using PWA. Respiratory disturbance index (RDI) and A were randomly scored twice by the same observer in 12 male patients with SAS. The first scoring was done using conventional PSG signals, the second scoring adding PWA to PSG. We also measured interobserver agreement by randomly selecting and reading 100 PSG sequences of 5 min with and without PWA by two observers. Adding PWA to PSG parameters allowed to detect significantly more RDI (53.9 +/- 21.6 h(-1) versus 48.3 +/- 22.3 h(-1), p < 0.001) and more A (68.0 +/- 14.4 versus 59.4 +/- 16.5, p < 0.001). Moreover, after using PWA, there was no significant disagreement between two observers for detecting RE, showing better quality of RE detection. PWA is a simple and cheap parameter that improves the diagnostic value of conventional PSG in sleep apnea syndrome by better detecting respiratory events and A.