Vitamin D has been mentioned in the literature has a potentially important agent for preventing the development of tumors, namely breast, colon, prostate and ovary tumors. However, the currently available evidence on the subject is contradictory and inconclusive. In this Cochrane systematic review, patients taking supplemental vitamin D on its various forms (cholecalciferol, ergocalciferol, alfacalcidol or calcitriol), regardless the dose, duration and route of administration, were compared with placebo, healthy adults without any intervention or adults with a disease in a stable phase, non-related with vitamin D metabolism. The results showed that currently, there is no firm evidence that vitamin D supplementation increases or decreases the risk of cancer occurrence, mainly in elderly community-dwelling women. Though at risk of type I errors due to small samples and substantial dropout of participants during the trials, the administration of supplemental cholecalciferol led to a 12% (CI 95%: 2 a 22%) decreased in cancer mortality, while the administration of supplemental vitamin D decreased all-cause mortality by 7% (CI 95%: 2 a 12%). The combined administration of supplements of cholecalciferol and calcium induced an increased incidence of nephrolithiasis.