Obstructive sleep apnea (OSA) is associated with the progression of cardiovascular disease (CVD), particularly in the middle-aged population. However, the clinical importance of OSA as a risk for CVD in the elderly population remains controversial. Moreover, evidence for the effectiveness of continuous positive airway pressure (CPAP) treatment for the secondary prevention of CVD in elderly patients is lacking. We assessed whether CPAP treatment improves cardiovascular outcomes in elderly patients with OSA and CVD. In this retrospective cohort study, we enrolled 130 elderly patients aged 65-86 years with moderate to severe OSA (apnea-hypopnea index ≥15/h) and a history of hospitalization due to CVD, who underwent polysomnography between November 2004 and July 2011. Patients were divided into the CPAP group (n = 64) or untreated OSA group (n = 66). The main outcome measures were cardiovascular death and hospitalization due to CVD. During the mean follow-up period of 32.9 ± 23.8 (standard deviation) months, 28 (21.5 %) patients either died or were hospitalized. The Kaplan-Meier curves indicated that event-free survival was significantly lower in the untreated OSA group than in the CPAP group (P < 0.005). A multivariate analysis showed that the risk was significantly increased in the untreated OSA group (hazard ratio 5.13; 95 % confidence interval 1.01-42.0; P < 0.05). Moderate to severe OSA not treated with CPAP was an independent risk factor for relapse of a CVD event, and adequate CPAP treatment improved cardiovascular outcomes in elderly patients.