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Previous studies have demonstrated that rural Gambian children have poor growth, delayed puberty and low bone mineral status. Their calcium intake is low (300 - 400 mg/d). This study examined the benefit of an increase in calcium intake on growth and bone mineral development in Gambian children. 160 subjects, aged 8-12 years old (80 M, 80 F) were recruited into a randomised, double-blind, placebo-controlled study of calcium supplementation. Bone mineral status was evaluated using single photon absorptiometry of the radius, and ultrasound measurements at the calcaneus. Anthropometry was performed and pubertal status assessed. Dietary intake was measured, and information on subject characteristics, physical activity and lifestyle factors were obtained. Fasting blood and 24h urine were collected for measurement of biochemical indices of calcium and bone metabolism. Data was collected at baseline, after 12 months of supplementation (714 mg Ca /d) and 12 months after withdrawal of the supplement. Analysis of baseline data showed there were no differences in subject characteristics and bone variables between boys and girls, except that girls had significantly greater triceps skinfold thickness (p≤0.0001). There were no significant differences between the supplemented and placebo groups in subject characteristics, anthropometry or bone variables at baseline. The Gambian children were smaller by ≥1 SD for their age compared with British reference children and the majority were prepubertal. At outcome, the supplemented group had significantly higher BMC, BMD and size- adjusted BMC at the mid-shaft and distal radius compared with the placebo group. No differences were observed in response between boys and girls or at different ages or pubertal status. There was no significant effect of the calcium supplement on weight, height or bone width. At follow-up, the supplemented group still had significantly higher BMC, BMD and size-adjusted BMC at the mid-shaft radius and, although not significant, a similar trend was seen at the distal radius. The calcium supplemented group had significantly lower concentrations of plasma osteocalcin, parathyroid hormone, phosphate, lower urinary titratable acid and phosphate outputs, and had a greater urinary calcium output than the placebo group at outcome. At follow-up the only difference remaining was a lower PTH in the calcium supplemented group. The results suggest that Gambian children on a low calcium diet may benefit from a higher calcium intake by lowering bone turnover rate. Further studies are needed to determine the long-term benefit of calcium supplement on bone mineral acquisition of Gambian children.