Bone mineral density (BMD) was evaluated by dual energy x ray absorptiometry in 60 adults (33 males, 27 females; aged 50, range 23-76 years) who were growth hormone deficient from various causes for 10.4 (1-31) years. Adult patients who had acquired growth hormone deficiency before completion of puberty had significantly reduced mean (SEM) BMD compared with age matched healthy controls at the lumbar spine: 0.87 (0.09) v 1.20 (0.03) g/cm2, femoral neck: 0.81 (0.06) v 1.08 (0.04) g/cm2, and Ward's triangle: 0.68 (0.07) v 1.04 (0.05) g/cm2. These values were also reduced compared with those of patients who had received human growth hormone during puberty. Untreated growth hormone deficiency when present during puberty results in reduced adult bone density.