The aim of our study was to determine whether the c.-223C > T (rs2073617) polymorphism in the 5′UTR region of the gene encoding osteoprotegerin is a functional polymorphism which may change the gene expression and resulting OPG levels, and so be associated with osteopenia and osteoporosis, and impaired bone metabolism in Crohn’s disease and ulcerative colitis patients. The gene discussed is TNFRSF11B; the disease is Crohn disease.