Objective: In this study, we compared the changes in arterial stiffness in chronic hemodialysis patients treated with 8-h vs. 4-h thrice weekly in-center hemodialysis. Methods: Sixty prevalent chronic hemodialysis patients assigned to 8-h nocturnal in-center thrice weekly HD (NHD) and 60 control cases assigned to 4-h thrice weekly conventional HD (CHD) were followed for one year. Radial-carotid pulse wave velocity, augmentation index and echocardiography were performed at baseline and 12 th month. Results: Mean age of the patients was 49 ± 11 years, 30.8% were female, 27.5% had diabetes mellitus and mean dialysis vintage was 57 ± 47 months. Baseline demographical, clinical and laboratory parameters were similar between groups. During a mean follow-up of 15.0 ± 0.1 months, blood pressure remained similar in both groups while the number of mean daily anti-hypertensive substances decreased in the NHD group. In the NHD group, time-averaged serum phosphorus and calcium-phosphorus product were lower than the CHD group. Pulse wave velocity and augmentation index decreased in the NHD group (from 11.02 ± 2.51. m/s to 9.61 ± 2.39. m/s and from 28.8 ± 10.3% to 26.2 ± 12.1%; p=0.008 and p=0.04, respectively). While augmentation index increased in the CHD group (28.0 ± 9.4 to 31.0 ± 10.7%, p=0.02), pulse wave velocity did not change. Subendocardial viability ratio and ejection duration improved in the NHD group (from 135 ± 28 to 143 ± 25%, p=0.01 and from 294 ± 34. ms to 281 ± 34. ms, p=0.003, respectively), accompanied by regression of left ventricular mass index. In multiple stepwise linear regression analyses, NHD was associated with improvements in augmentation index, ejection duration and subendocardial viability ratio. Conclusions: These data indicate that arterial stiffness is ameliorated by implementation of longer hemodialysis sessions. © 2011 Elsevier Ireland Ltd.