Continuous positive airway pressure (CPAP) treatment improves endothelial function and sympathetic activity in patients with obstructive sleep apnea (OSA). However, the long-term effects of CPAP on pulse wave velocity (PWV), which reflects arterial stiffness that is associated with cardiovascular events, have not been evaluated in OSA patients with or without hypertension (HT). In this study, 212 male OSA patients who had been receiving CPAP treatment for 2 years and were divided into two groups, those with HT (n=114) and those without (n=98), were studied. In both HT and normotensive (NT) patients, PWV decreased significantly over the first 6 months of treatment (P=0.005 and 0.010, respectively), before increasing gradually from 6 to 24 months. Body mass index (BMI), body weight, heart rate (HR), systolic blood pressure (SBP) and diastolic blood pressure (DBP) levels decreased significantly in the HT group over the 2 years of CPAP treatment (P<0.001 for all). In contrast, only HR decreased significantly in the NT group over the 2 years of treatment (P<0.001). Multivariate regression analysis revealed that age (P=0.008), decreases in DBP (P<0.001) and HR (P<0.001) and higher initial levels of serum high-density lipoprotein-cholesterol (P=0.040) were independent factors related to changes in PWV over the 2 years of CPAP treatment in all patients. In conclusion, we found a significant decrease in PWV in both NT and HT patients after 6 months of CPAP treatment. In HT patients, long-term CPAP treatment significantly decreases blood pressure, which may contribute to explain the PWV improvement.