BACKGROUND: During the mid to late 20th century, parts of Europe and North America began experiencing increasing incidence of inflammatory bowel disease for unknown reasons. Epidemiological studies carried out at the time determined that incidence rates and disease severity were higher in the northern latitudes than in the southern latitudes. LITERATURE REVIEW: In the ensuing years, an inverse association was established between ultraviolet radiation and incidence of Crohn’s disease, a finding that has not proven to be as robust for ulcerative colitis. This association was explored further and vitamin D was implicated to be the factor of ultraviolet radiation which was associated with increased incidence. Currently, all evidence implicating vitamin D in the pathogenesis of Crohn’s disease comes from epidemiological, animal, and in vitro studies, providing strong evidence for an association, but none of which can prove causality. Causality must be proven in prospective clinical trials, which, at present, have come up short in providing statistically significant findings. METHODS: The proposed trial outlined below provides a method of studying the question at hand in a way that has not been previously studied. This is a randomized, double blind, controlled trial which assesses the effect of supplementation of vitamin D in patients with active Crohn’s disease. DISCUSSION: Acceptance of the alternative hypothesis would be a big step forward in the management of Crohn’s disease. It would have wide-ranging implications, resulting in decreased healthcare costs, decreased use of toxic medications, and increased quality of life.