Dialysis patients have an increased burden of cardiovascular disease, with >70% of patients dying from a cardiovascular event. Several recent retrospective cohort studies have shown an association of treatment with calcitriol or its analogs and improved survival. The similar findings of these studies increase the validity of the observations, but these studies are subject to biases inherent in this type of study design. In particular, the nonrandom choice to treat, lack of information on concomitant medications, and differences in characteristics of patients who are treated compared with those not treated can lead to significant bias. Thus, prospective studies are needed. Two, small, uncontrolled, prospective studies showed improvement in left ventricular hypertrophy in dialysis patients treated with α-calcidiol or calcitriol, and there is abundant animal and in vitro studies showing biological plausibility. Thus, given the available evidence, it seems prudent to advise that most dialysis patients receive some form of vitamin D while we await results of a prospective interventional trial. The unknown is what type and how much to give, and whether this approach is safe, especially in patients with low levels of PTH.