Summary Introduction. The purpose of this study was to evaluate the effects of intensive sport training on the bone mineral density in a group of elite prepubertal girls. These girls were engaged either in sports requiring significant impact loading on the skeleton (gymnastics), or not (swimming). Method. Forty-one healthy girls (10–11 years old) took part in this study. The group included ten swimmers and 18 gymnasts who had performed 3 years of high level sport training (8–15 hours a week on average) and 13 non-exercising controls. Bone mineral content (BMC) or density (BMD) measurements were done using dual-energy X-ray absorptiometry. Results. There was no statistically significant difference between groups for age, bone age, height and body composition. There was no statistically significant difference between swimmers and controls for all the BMD measurements. BMD in gymnasts were statistically higher than in the control group for non-dominant radius, L2–L4 vertebrae, femoral neck and Ward's triangle. Identical results were done for BMC data when adjusted to body weight. Conclusion. We conclude that physical activity in childhood could be an important factor of bone mineral acquisition in prepubertal girls, only if the sport can induce bone strains during a long term program.