The primary objective of this study is to establish optimal oral calcium supplementation in Crohn's patients who have had an ileal bowel resection. This population is at high risk for calcium oxalate kidney stones, a direct consequence of extensive gut malabsorption and enteric hyperoxaluria. The benefit of providing oral calcium in this patient population (as a means to reduce intestinal oxalate absorption) is known, however, there are no appropriate targets for calcium dosing, which is presently performed empirically or not at all. Our goal is to establish simple, safe and practical guidelines for calcium supplementation.