INTRODUCTION: Adherence to therapy is a relevant challenge in chronic hemodialysis patients. The directly observed therapy (DOT) could be an effective method to increase adherence for specific therapies. We aimed to study the performance of DOT versus home medication. We follow the impact of providing native vitamin D directly by the nurse after a dialysis session on the 25-hydroxyvitamin [25(OH)D] concentrations. METHODS: In this observational study, we included 38 dialysis patients treated by stable dosage of cholecalciferol. DOT was implemented in December 2010. We considered the concentrations of 25-OH vitamin D three times before (T1 = June 2010, T2 = July 2010 and T3 = September 2010) and three times after the modification of prescription (T4 = February 2011, T5 = March 2011 and T6 = April 2011). RESULTS: Median age was 72 [62; 79] years and 48 % were diabetics. Mean body mass index was 26 ± 5 kg/m(2) and median dialysis vintage was 20 [8; 46] months. The patients were compared to themselves. Before DOT, median concentrations of 25(OH)D were 27 (14-36), 23 (17-31), 31 (22-38) ng/mL at T1, T2 and T3, respectively. When DOT was effective, the concentrations significantly increased to 34 (28-44), 35 (29-41), 39 (32-47) ng/mL at T4, T5 and T6, respectively. Before DOT, 19 patients (50 %) reached the target of 30 ng/mL. After DOT, 29 patients (76 %) reached the target concentration of 30 ng/mL. CONCLUSIONS: In hemodialysis patients, DOT is both simple and effective to increase the therapeutic impact to native vitamin D.