As the actual mortality and morbidity of obstructive sleep apnea syndrome (OSAS) have been unknown heretofore, we undertook a follow-up study of 198 OSAS patients seen at the Stanford Sleep Disorders Clinic between 1972 and 1980, for whom either tracheostomy (71 patients) or weight loss (127 patients) had been recommended. At five-year follow-up, all of the deaths (14) had occurred among those conservatively treated with weight-loss (a mortality rate of 11 per 100 patients per five years). These patents also had a higher five-year crude vascular mortality rate: 6.3 per 100 patients per five years, with an age-standardized vascular mortality rate of 5.9 per 100 patients per five years (95 percent confidence interval [CI] 2.5-11.6) vs 0 per 100 for the surgically treated population; this despite a lower mean apnea index (43 versus 69) and a lower mean body mass index (31 versus 34 kg/m2) in the conservatively treated group. With the fictional adjunction of one possible death at five-year follow-up in the surgically treated group, the age-adjusted odds of vascular mortality at five years for the conservatively treated group was 4.7. Our data therefore encourage "aggressive" treatment for patients with OSAS.