Childrens' need for calcium is uncertain, and as a consequence there are large differences in the official recommendations for calcium intake. A low calcium intake is not followed by acute complications. A very low calcium intake (less than 200 mg/d) combined with a high intake of fibre and phytate can cause osteomalacia, as in rickets. Several studies support that calcium intake during growth is positively associated to bone mineralisation, and to peak bone mass, which is associated to the risk of developing osteoporosis. At present, we know very little about childrens' ability to adapt to a low calcium intake. Furthermore, knowledge of the capacity for catch-up mineralisation after a period of low calcium intake is limited. Bone mineralisation during growth is also influenced by physical activity, hormonal status and race. The relative importance of these factors is unknown. Longitudinal studies of bone mineralisation using DXA scanning will, in the future, increase our knowledge about the need for calcium during growth.