The physiological roles of vitamin D in the functioning of the immune and inflammatory systems have been the subject of intense research over the past decade and have stimulated interest in the connections between this steroid hormone and sepsis. While the science directly examining the relationship between sepsis and vitamin D is still emerging, many inferences can be made from current literature from various scientific disciplines looking at the seasonal, geographical and racial patterns of infections and vitamin D deficiency. This review will explore these associations, drawing from the fields of ecology, epidemiology and clinical research and describe the potential causal relationships implicated by the basic sciences.