BACKGROUND: Vitamin D compounds are widely used to prevent and treat secondary hyperparathyroidism. PURPOSE: To determine whether vitamin D therapy improves biochemical markers of mineral metabolism and cardiovascular and mortality outcomes in chronic kidney disease. DATA SOURCES: MEDLINE (January 1966 to July 2007), EMBASE (January 1980 to July 2007), and Cochrane databases were searched without language restriction. STUDY SELECTION: Randomized, controlled trials of vitamin D compounds in chronic kidney disease were identified. DATA EXTRACTION: Two authors independently extracted data. DATA SYNTHESIS: Seventy-six trials were identified for inclusion; 3667 participants were enrolled. Vitamin D compounds did not reduce the risk for death, bone pain, vascular calcification, or parathyroidectomy. Compared with placebo, established vitamin D sterols were associated with an increased risk for hypercalcemia (relative risk, 2.37 [95% CI, 1.16 to 4.85]) and hyperphosphatemia (relative risk, 1.77 [CI, 1.15 to 2.74]) but did not show a consistent reduction in parathyroid hormone (PTH) levels. Compared with placebo, more recently developed vitamin D analogues were associated with hypercalcemia (relative risk, 5.15 [CI, 1.06 to 24.97]) but not hyperphosphatemia, and levels of PTH were reduced (weighted mean difference, -10.77 pmol/L [CI, -20.51 to -1.03 pmol/L]). For suppression of PTH, intravenous administration was superior to oral vitamin D, but higher intravenous doses were used. LIMITATIONS: Few studies reported patient-level outcomes, including mortality (8 of 76 trials), and only 5 trials directly compared the effects of treatment with newer vitamin D compounds versus established ones. Heterogeneity in some comparisons remained unexplained by metaregression analyses. CONCLUSION: Vitamin D compounds do not consistently reduce PTH levels, and beneficial effects on patient-level outcomes are unproven. The value of vitamin D treatment for people with chronic kidney disease remains uncertain.