Patients with obstructive sleep apnea (OSA) are susceptible to developing atherosclerosis. Consequently, such patients are at a high risk of developing cardiovascular diseases, leading to poor prognosis. Many physiological parameters have been previously used to predict the development of atherosclerosis. One such parameter, the cardio-ankle vascular index (CAVI), a measure of arterial stiffness, has garnered much attention as it can also predict the degree of atherosclerosis. The CAVI can be calculated based on noninvasive measurements, and is less susceptible to blood pressure variations at the time of measurement. Therefore, the CAVI can assess changes in arterial stiffness and the risk of developing atherosclerosis independent of blood pressure changes. Continuous positive airway pressure (CPAP) is a standard therapy for OSA and can suppress the issue significantly. Several studies have shown that CPAP treatment for OSA could also reduce the CAVI. In this review, we discuss the relationship between OSA and arterial stiffness, primarily focusing on the CAVI. Furthermore, we propose future perspectives for the CAVI and OSA.