People with cystic fibrosis (CF) now frequently live into adulthood and with this extended life expectancy has come new clinical problems. Poor bone health, including osteoporosis and bone fractures, is one of these increasingly important conditions. Preventing the negative outcomes of poor bone health in later life is primarily related to ensuring optimal growth (weight and height) and obtaining maximal amount of bone mass during growth and development. This study will identify factors that influence bone health in a sample of children, adolescents and young adults as measured by dual energy x-ray absorptiometry and new bone densitometry methods (peripheral quantitative computerized tomography [p-QCT] and bone sonometer). We will also identify factors which influence changes in bone status over a 12-month follow-up period in a subsample of people with CF.