Background. Patients with chronic kidney disease (CKD) are at high risk for atherosclerotic cardiovascular disease (ACVD). In addition to the same epidemiological risk factors of the general population, factors unique or secondary to the uremic milieu may contribute to excess cardiovascular morbidity and mortality. Recent studies suggest the endothelium has a key role in the development of atherosclerosis. Circulating endothelial cells (CECs) may be a tool to study the state of the endothelium, with their number markedly increased in conditions associated with a high degree of endothelial cell activation and/or injury. Our hypothesis is that CEC number increases in diseases that commonly progress to stage 5 CKD, as well as in patients on hemodialysis (HD) therapy, reflecting ongoing endothelial cell activation and/or injury. Methods: The study population consisted of 22 healthy nonsmoking individuals, 29 individuals undergoing long-term HD treatment, 10 individuals with the diagnosis of diabetes mellitus and stage 1 or 2 CKD, and 7 individuals with hypertension and stage 1 or 2 CKD. The number of CECs was enumerated in all study groups. Results: We found that CEC number was increased in HD patients, hypertensive patients, and patients with diabetes compared with healthy individuals. In addition, although CEC number did not accurately reflect the presence of ACVD, the number was increased significantly in a group of HD patients with active ACVD, whereas it was decreased significantly in a group of HD patients with stable ACVD. Conclusion: Our results suggest that CEC number may reflect ACVD activity in HD patients, independent of the presence of ACVD.