Background: The changes in kidney functions, adversely affect the cardiovascular system. The aim of this study was to investigate whether arterial stiffness (AS), an indicator of subclinical atherosclerosis, was affected in patients with congenital or acquired reduced renal mass. Methods: In this prospective study, a total 135 patients (mean age 43.4 ± 8.5 years and 71.9% female) with congenital unilateral small/nonfunctioning kidney or unilateral agenesis or with unilateral nephrectomy were included. As control group, 44 healthy individuals with similar age and gender (mean age, 42.5 ± 7.1 year and 61.4% female) were included. Estimated glomerular filtration rate (eGFR) was calculated by Modification of Diet in Renal Disease formula. Official blood pressures (BP) and 24-h ambulatory noninvasive BP of both groups were measured. AS was assessed with pulse wave velocity (PWV) by using Mobile-O-Graph new genaration arteriograph device using oscillometrical method. Results: There was no difference in terms of BP parameters and body mass index between groups. eGFR values of control group and study group were 93 ± 19 ml/min/1.73 m² and 89 ± 28 ml/min/1.73 m², respectively (p = 0.379). Compared with control group, the study group had higher PWV values (6.72 ± 1.11 m/s vs. 6.29± 0.75 m/s, p = 0.018). In linear regression analysis, PWV was found to be correlated with age (β = 0.752, p < 0.001), and daytime ambulatory systolic BP (β = 0.345, p < 0.001). Conclusion: Our study showed that AS was increased in patients with reduced renal mass and this increase in AS was related to age and systolic BP. No relation was determined between AS and eGFR.