['To examine the hypothesis that respiratory events in obstructive sleep apnea syndrome (OSAS) end in arousal not detected by conventional electroencephalographic (EEG) leads.', 'Observational.', 'The study was conducted at a major metropolitan sleep disorders center.', '10 patients with untreated OSAS and 5 patients undergoing continuous positive airway pressure (CPAP) titration for OSAS.', 'Standard clinical nocturnal polysomnography recordings were supplemented to include frontal EEG leads and airflow measured by nasal cannula pressure. In 10 untreated subjects, 1465 obstructive events (apneas, hypopneas, and flow limitation events), and in 5 subtherapeutic CPAP-titrated subjects, 459 total events were identified during non-rapid eye movement (REM) sleep only. American Academy of Sleep Medicine arousal criteria applied to central leads and to frontal leads allowed detection of an additional 24% respiratory event-related arousals by frontal leads than by conventional leads. Frontal arousal detection differed by event type: 16% of apneas, 21% of hypopneas, and 35% of flow limitation events. Autonomic correlate (increased heart rate) of both conventional and frontal arousals was similar (in a subgroup of 8 untreated patients, analyzing only flow limitation events). Tabulating frontal arousals separately for each frontal lead indicated that Fz as the sole frontal lead (added to conventional leads) increased detection of arousals by 19% over using only conventional leads (total of 92% of all obstructive respiratory events).'] Does the addition of frontal EEG lead improves detection of cortical arousal following obstructive respiratory events?