Bone mineral content was measured by dual-energy x-ray absorptiometry in the lumbar spine at the L2-L4 level with a Lunar DPX densitometer model in 471 healthy white Mediterranean Spanish children and adolescents (256 boys and 215 girls) randomly selected from the urban area of Barcelona. Ages ranged from 3 mo to 21 y. Weight, height, and pubertal development were in the normal age distribution. Bone mineral content values were corrected by the vertebral surface area scanned and expressed as bone mineral density (BMD) values. BMD increased progressively from infancy to adulthood, and values were similar in both sexes, with the only differences related to the earlier onset of puberty in girls. A statistically significant correlation (p < 0.001) was found between BMD values and age, height, and weight. BMD values increased annually, but the periods of higher increase were observed during the first 3 y of life and late puberty. A significant (p < 0.001) increase in BMD was observed between Tanner pubertal stages III and IV and between Tanner stage IV and adult values. Lumbar BMD values peaked in a similar way to growth height velocity during pubertal development. However, the BMD peak seemed to occur somewhat later than height velocity peak, particularly in girls. In conclusion, we report normative data for BMD values at the lumbar level in our normally growing pediatric population and show that the first 3 y of life and adolescence are critical periods for bone mineralization. These data provide a tool for the investigation and follow-up of pediatric populations at risk for low bone mineralization.