Effective treatment with nasal continuous positive airway pressure (nCPAP) lowers blood pressure (BP) in patients with obstructive sleep apnea (OSA). It was reported that OSA might influence BP in middle-aged but not in elderly patients. However, effects of nCPAP treatment in elderly hypertensive OSA patients are not well known. We investigated long-term compliance with nCPAP and its effects on BP in elderly and middle-aged OSA patients. This observational study involved 92 OSA patients (81 men, 11 women; 46 middle-aged, 46 elderly; body mass index (BMI), 27.7 (27.0-28.7) kg m(-2); apnea hypopnea index, 43.0 (39.4-46.6) per h; 95% confidence intervals). BP and BMI were measured before the study and at two checkpoints after usage of nCPAP (616 (553-679) and 1048 (985-1114) days). Diastolic BP decreased by 5.69 (3.09-8.29) mm Hg after 600 days of nCPAP treatment and by 4.50 (1.80-7.19) mm Hg after 1000 days (P=0.003). There were no significant changes in systolic BP, BMI or usage time of nCPAP. With a daily average of 3 h or more of nCPAP treatment, diastolic BP decreased significantly in subject groups ≥ 60 and <60 years of age. Even in the elderly, a daily average use of nCPAP for 3 h would lower diastolic BP in OSA patients.