Longitudinal bone mineral changes after renal transplantation were studied in 14 children aged 8 +/- 4 years. Combination immunosuppressive therapy was given to all patients (prednisone, azathioprine, cyclosporine). Bone mineral density (BMD) measurements of the first through fourth lumbar vertebrae by dual-energy X-ray absorptiometry were performed within 1 year preceding renal transplantation and 6, 12, and 24 months afterward (M0, M6, M12, and M24, respectively). The results of BMD obtained in grams of hydroxyapatite per square centimeter of spine projected area were subsequently transformed to standard deviation scores for a normal pediatric population. In addition, we used a mathematical spine volume correction to give the results in grams per cubic centimeter. All patients had a well-functioning renal graft at M6, M12, and M24 and a normal serum creatinine level. Significant decreases in BMD, standard deviation score, and spine volume-corrected BMD were observed 6 months after renal transplantation (p < 0.05, p < 0.01, and p < 0.01 respectively); the median loss of BMD and spine volume-corrected BMD was 9.2% and 15.6% at M6, respectively, and the median serum parathyroid hormone level dropped from 125 to 34 pg/ml. Between M6 and M12, BMD increased significantly up to 95% (median) of pretransplantation values and reached 97.2% (median) at M24. Similar but less marked improvement was observed in spine volume-corrected BMD results, reaching 87.7% and 87.4% at M12 and M24, respectively. A negative correlation was found between the cumulative prednisone dose and BMD in grams per square centimeter at M6 (r2 = 0.603; p = 0.006), M12 (r2 = 0.532; p = 0.015), and M24 (r2 = 0.40; p = 0.014). There was no correlation between cumulative prednisone dose and spine volume-corrected BMD or standard deviation score. Mean 6-month cyclosporine levels did not correlate with any measure of BMD. We conclude that after renal transplantation children have a significant decrease of BMD during the first 6 months after the operation, despite normal graft function and growth improvement.