Introduction: There are limited data available on bone mass status in Spanish children and or whether the differences are associated with diet/hygiene habits or geographical variability. Subjects and methods: To determine this association a cross-sectional study was carried out in three different areas (northern, central and southern Spain) and included 1176 schoolchildren between 5 and 12 years old, randomly selected from schools in those areas. Bone density of the distal phalanges was measured by bone ultrasound. We examine the correlations between these data and calcium and vitamin D intake, physical activity and bone mass index. Results: Of the 1176 children initially included, 1035 nutritional questionnaires were completed and bone ultrasound data were obtained on 991 of them. Eighteen percent of girls and 13% of boys had a calcium intake below 800 mg per day. More than 70% of children have a daily vitamin D intake under 2.5 mcg. Age and exercise showed a direct linear relationship with bone mineral density, and an inverse one for overweight. Conclusions: Both high physical activity and high calcium intake were associated with a higher bone mineral density, while overweight showed the opposite effect. Diet habits and exercise must be considered the main strategies to prevent adult osteoporosis during childhood. (C) 2010 Asociacion Espanola de Pediatria. Published by Elsevier Espana, S.L. All rights reserved.