Obstructive sleep apnea (OSA) is a risk factor for cardiovascular death in middle-aged subjects, but it is not known whether it is also a risk factor in the elderly. To investigate whether OSA is a risk factor for cardiovascular death and to assess whether continuous positive airway pressure (CPAP) treatment is associated with a change in risk in the elderly. Prospective, observational study of a consecutive cohort of elderly patients (≥65 yr) studied for suspicion of OSA between 1998 and 2007. Patients with an apnea-hypopnea index (AHI) less than 15 were the control group. OSA was defined as mild to moderate (AHI, 15-29) or severe (AHI, ≥30). Patients with OSA were classified as CPAP-treated (adherence ≥ 4 h/d) or untreated (adherence < 4 h/d or not prescribed). Participants were monitored until December 2009. The end point was cardiovascular death. A multivariate Cox survival analysis was used to determine the independent impact of OSA and CPAP treatment on cardiovascular mortality. A total of 939 elderly were studied (median follow-up, 69 mo). Compared with the control group, the fully adjusted hazard ratios for cardiovascular mortality were 2.25 (confidence interval CI, 1.41 to 3.61) for the untreated severe OSA group, 0.93 (CI, 0.46 to 1.89) for the CPAP-treated group, and 1.38 (CI, 0.73 to 2.64) for the untreated mild to moderate OSA group. Severe OSA not treated with CPAP is associated with cardiovascular death in the elderly, and adequate CPAP treatment may reduce this risk.