Prevention, or at least delay in onset of type 2 diabetes is possible by intensive lifestyle intervention. This is costly and labour intensive, and alternative methods of preventing diabetes have been sought. Vitamin D has important physiological effects aside from its effects on bone metabolism, including an important role in glucose homeostasis, insulin release and response. Observational data strongly support the role of vitamin D deficiency in the pathogenesis of type 2 diabetes. The time is ripe for a well conducted randomised controlled trial of vitamin D in high risk individuals to test the hypothesis that vitamin D delays the onset of type 2 diabetes.