Li J, et al. - We investigated the prevalence of vitamin D deficiency and low bone mineral density (BMD) among children, especially those in developing countries. They also assessed the association of serum 25-hydroxyvitamin D [25(OH)D] with BMD among children. A positive and significant association of age, weight, and height with total body less head (TBLH) BMD was seen in linear regression analysis. The strongest determinant of TBLH BMD was age in boys and weight in girls. Serum 25(OH)D concentrations were not significantly associated with BMD obtained for total body and at various skeletal sites (r ranged from -0.005 to 0.014) regardless of whether children evaluated were sufficient, insufficient, or deficient in vitamin D. Vitamin D deficiency was seen in more than one-third of children and adolescents in a Northwest Chinese city but low BMD developed in only <2% of them.