With dual energy X-ray absorptiometry (DEXA), it is possible to quantitate important aspects of growth in children with cystic fibrosis (CF), supplementing the usual measures of height and weight. Of particular concern during growth is the accumulation of bone mineral, since osteoporosis and fractures are well-recognized problems in end-stage disease. Various measures of growth and body composition were examined in 40 children and young adults (ages 5.7-20.3 years, mean 11.9 years) and compared to age-, gender-, and race-matched normal controls. The mean (+/- SE) weight Z-score of the 40 CF patients was -0.70 +/- 0.11, and the mean height Z-score was -0.66 +/- 0.15. Relative to their matched normal controls, the CF patients had a deficit in total body bone mineral averaging 19.1% +/- 3.0%. The deficits in total body bone mineral correlated with pulmonary and nutritional measures of disease severity. Serum vitamin D levels, calcium intake, age, gender, use of steroids, and CF genotype were not found to be significant factors. In this group of children and young adults with CF, height and weight measures of growth were not dramatically reduced (mean Z-scores = -0.7), yet large deficits in total body bone mineral averaging nearly 20% were identified.