The goal of this study was to evaluate the prevalence of poor bone mineralization in children and young adults with Crohn's disease, correlates of low bone density, and the effect of six months of calcium supplementation on bone mineral density in children with Crohn's disease with low bone density. One hundred and thirty-two subjects with Crohn's disease and fifty-one healthy controls were evaluated. Assessments included growth, body composition, bone mineral density, skeletal and sexual maturation, dietary intake, serum vitamin D levels, biomarkers of bone turnover, medication use, and disease severity indicators. Following baseline evaluation, children (ages 5-18 years) with Crohn's disease and low bone density (spine z-score < -1.0) were invited to participate in a double-blind, randomized, placebo-controlled study of calcium supplementation. Fifty six subjects completed the intervention study. All data collection and lab analyses are complete. Data analysis and manuscript preparation are ongoing.