Compare correlation of pQCT parameters and BMD as measured by DXA to markers of bone turnover and inflammation (serum propeptide of type I collagen (PICP), total serum deoxypyridinoline, C-reactive protein (CRP), interleukin 6 (IL-6), and tumor necrosis factor (TNF)-alpha) in children with CF 6-12 years of age and healthy controls. As an exploratory specific aim, the correlation between these serum markers and the bone measurements in Specific Aim 1 will be evaluated.