Vitamin D status is one of the major factors that may prevent progression of secondary hyperparathyroidism in patients with CKD. Insufficient levels of 25-hydroxyvitamin D further exacerbate secondary hyperparathyroidism by not providing adequate substrate for the renal 1-alpha-hydroxylase for conversion to the active form of vitamin D, 1,25(OH)2D. A recent cross-sectional study on patients with moderate to severe CKD not yet on dialysis therapy from 12 geographically diverse regions of the United States has shown that only 29% and 17% of them had sufficient level, respectively (13). Vitamin D status is easily corrected. In our previous study we concluded that weekly cholecalciferol supplementation was an effective treatment to correct vitamin D status in patients with CKD stages III and IV (14). However, PTH levels did not return to normal. Therefore, it is likely that earlier intervention with vitamin D is necessary to prevent rather than to treat secondary hyperparathyroidism. This is the major question that is being evaluated in this study. Can intervening with vitamin D at an earlier stage of chronic kidney disease result in decreased incidence of secondary hyperparathyroidism?