Patients with sleep apnea syndrome (SAS) show cardiac dysrhythmias in association with cyclical nocturnal hypoxemia; are they at risk of dying during sleep? To assess this claim, we reviewed the clinical course of 91 patients with polysomnographically documented SAS between July 1978 and June 1986. A control group was comprised of 35 patients who were referred with symptoms suggestive of SAS but had negative sleep studies. Follow-up was obtained by survey questionnaire. Nine of 91 SAS and four of 35 control patients had died by completion of the study. There were no statistically significant differences in mortality between the two groups. None of the SAS patients died in their sleep, but they reported a higher incidence of disability and vehicular mishaps than did control subjects. The findings in this study do not support the hypothesis that SAS patients are at increased risk of dying in their sleep.