To determine clinically useful predictors of calcium retention during postpubertal growth, calcium balance, bio-chemical markers of bone turnover, and anthropometric variables were determined in 14 girls aged 11-14 y and in 11 young women aged 19-30 y. Subjects participated in a 3-wk calcium-balance study with a calcium intake of 1332 mg/d. Biochemical markers of bone turnover (serum osteocalcin, total alkaline phosphatase, bone alkaline phosphatase, tartrate-resistant acid phosphatase, and urinary cross-linked N-teleopeptides of type I collagen and hydroxyproline as the creatinine ratios) were measured in fasting samples. Total-body bone mineral density and total-body calcium content were significantly higher in adults than in adolescents (1.17 compared with 1.05 g/cm2 and 1019 compared with 791 g, respectively). At the observed retention of 326 mg/d, adolescents would require 2 y to reach the total bone calcium of the young adults. All biomarkers of bone turnover were strikingly higher in adolescents than in adults and were strongly correlated with calcium retention. A multiple-regression model using a biochemical marker of bone turnover (serum osteocalcin) and postmenarcheal age (a measure of sexual maturation) described 75% of the variability in calcium retention.