Steroid treatment has several side effects, including the deterioration of the bone and mineral metabolism in children with nephrotic syndrome. This randomized prospective study was conducted to determine the effects and prophylactic role of calcium plus vitamin D treatment on bone and mineral metabolism in children receiving prednisolone treatment. 40 children (27 boys and 13 girls) with NS (18 new onset and 22 relapsing) were included in the study. Their mean age was 4.6+/-1.8 years. All patients received prednisolone treatment (2 mg/kg/day for 4 weeks followed by alternate days at the same dose for 4 weeks). The patients were randomized into treatment (vitamin D 400 IU plus calcium 1 g daily) and non-treatment groups. Bone mineral density, serum Ca, P, alkaline phosphatase and urinary Ca and P excretions were analyzed at the beginning and 2 months after the treatment. The XR36 Norland device was used for bone mineral density analysis. Bone mineral density was significantly decreased in both the treatment (0.54+/-0.15 to 0.51+/-0.1 g/cm(2), P =0.001) and non-treatment (0.52+/-0.18 to 0.45+/-0.16 g/cm(2), P <0.001) group. But the percentage of bone mineral density decrease was found to be significantly lower in the treatment group than in the non-treatment group (4.6+/-2.1% vs. 13.0+/-4.0%, respectively; P <0.001). Serum calcium and urinary calcium excretion increased in the treatment group (8.0+/-1.0 to 10.0+/-0.5 mg/dl and 1.1+/-0.5 to 3.2+/-1.0 mg/kg/day) and non-treatment group (8.1+/-0.8 to 10.0+/-0.6 mg/dl and 1.4+/-0.9 to 3.8+/-3.3 mg/kg/day) after prednisolone treatment (P <0.001). Steroid treatment decreases bone mineral density in children with nephrotic syndrome. Vitamin D plus calcium therapy at the current doses reduces but does not completely prevent bone loss, with no additional adverse effects.