The purpose of this study was to assess whether replacement doses of glucocorticoid hormones administered to patients with congenital adrenal hyperplasia (CAH) cause changes in body composition, including either generalized or regional osteoporosis. In 21 patients with 21-hydroxylase deficiency we measured height, body mass index, lean mass, fat mass, and whole body and regional bone mineral density (BMD). We measured the same parameters in 21 age- and sex-matched control patients. The CAH group (aged 8-32 yr) showed significantly reduced mean height compared with both standard data (P = 0.0015) and the control group (P = 0.009). There were no significant differences in mean body mass index between the CAH group and the standard data (P = 0.13) or the control group (P = 0.87). CAH males had significantly higher fat/lean mass ratios than control males (P = 0.005). There were no significant differences in whole body mean bone mineral apparent density values between the CAH and control groups (P = 0.39). There were, however, significant differences in whole body BMD z scores between the CAH and control groups and the reference data (P = 0.027 and P = 0.004, respectively). No significant differences were observed between the total CAH and control groups with respect to spinal bone mineral apparent density; however CAH males had significantly lower mean adjusted spinal BMD than the male controls (P = 0.02). We conclude that although replacement therapy with glucocorticoid and mineralocorticoid hormones in our group of CAH patients may not be optimal with regard to longitudinal growth, it is not deleterious in terms of general bone mineralization. It may decrease spinal BMD in CAH males. We also conclude that the relevance of Hologic reference data for BMD to an Australian population is uncertain, and there is a need for Australian standard data.