Objective: The aim of this study was to determine the effect of oral cholecalciferol treatment on vascular calcification, left ventricular mass index (LVMI) and other cardiac functions in dialysis patients. Design and methods: A six-month course of oral cholecalciferol treatment was recommended to dialysis patients with vitamin D insufficiency. While 26 patients were given cholecalciferol treatment, 17 patients who could not tolerate to therapy received standard therapy. Initial biochemical parameters were measured, and they were measured again after 6 months of treatment. Echocardiographic measurements were also performed, and the vascular calcification score (VCS) was calculated at baseline and at the 6th month. Results: The cholecalciferol replacement group showed no significant change in LVMI and VCS values (p > 0.05). However, while LVMI was similar between groups at initial evaluation, it was lower in the cholecalciferol group at the 6th month when compared to the standard treatment group (141.8 +/- 40.2 g/m(2) vs. 166.3 +/- 31.4 g/m(2); p = 0.04). Likewise, left ventricular diastolic diameters (48.8 +/- 5.1mm vs. 47.5 +/- 4.6 mm; p = 0.023) and left atrial diameters (41.2 +/- 8.9mm vs. 38.9 +/- 8.1 mm; p = 0.006) decreased in the cholecalciferol group. Additionally, significant increases were observed in serum 25-hydroxyvitamin D (25(OH)D) and albumin levels, with a significant decrease in serum C-reactive protein levels. Conclusion: A lesser increase in left ventricular mass and better diastolic functions was observed in dialysis patients after 6 months of cholecalciferol treatment.