This study aimed to investigate the relationship and prognostic significance of cardio-ankle vascular index, which is a measure of arterial stiffness that can lead to endothelial dysfunction and poor cardiovascular issues in COVID-19 patients, with COVID-19. The study included 115 patients, of which 65 patients in the case group with Real time reversetranscription-polymerasechainreaction test positive and diagnosed for COVID-19 and 50 volunteers in the control group. Patients with COVID-19 were classified as moderate/severe or mild COVID-19 in the subgroup analysis based on the severity of the disease. We investigated the relationship between cardio-ankle vascular index and COVID-19 by using the VaSera VS-1000 device to automatically measure each patient's cardio-ankle vascular index and ankle-brachial pressure index. The mean age of participants included in the study was 65.7±10.7 years. Patients and volunteers were statistically similar in terms of age, gender, comorbidities, Charlson comorbidity index scores, and body mass index values (p>0.05). The right-cardio-ankle vascular index value was 9.6±2.4 in the case group and 8.5±1.1 in the control group (p=0.004). The left-cardio-ankle vascular index value was 9.4±2.7 in the case group and 8.5±1.2 in the control group (p=0.01). The right-cardio-ankle vascular index value was 10.8±3.4 in the moderate/severe disease group and 8.8±0.9 in the mild disease group (p=0.008). The left-cardio-ankle vascular index value was 10.7±3.6 in the moderate/severe disease group and 8.5±1.5 in the mild disease group (p<0.001). The right-cardio-ankle vascular index and left-cardio-ankle vascular index values were found to be significantly higher in COVID-19 patients in our study. When receiver operating characteristic analysis was performed to distinguish moderate/severe COVID-19 patients from mild patients, right-cardio-ankle vascular index was area under the curve 0.757 (0.630-0.884), and left-cardio-ankle vascular index was area under the curve 0.782 (0.661-0.902). The right-cardio-ankle vascular index and left-cardio-ankle vascular index values increased in COVID-19 patients in our study, and this was thought to be prognostically significant.