1. Moderately overweight, premenopausal women were assessed for bone mineral density of the total body, lumbar spine and proximal femur before and after 6 months of modest dietary restriction (minimum 4800 kJ/day). The aim was to evaluate the effect of loss of body mass on bone mineral density. 2. Dietary assessment included two analyses of 3 day weighed food intakes, one before and the other after 4 months of dietary restriction. Energy and calcium intakes were significantly reduced by 27% and 5%, respectively. The change in calcium intake was negatively and significantly related to initial levels of calcium intake. 3. A significant mean loss of 3.4 +/- 3.1 kg in body mass was achieved mainly in the first 3 months of the study; it was accompanied by significant losses at 6 months in bone mineral density in the total body of 0.7% and in the lumbar spine of 0.5%. There were no changes in the femur. 4. The change in bone mineral density in the total body was significantly related to the reduced absolute calcium intake, initial bone mineral density and loss of body mass. The change in bone mineral density in the spine was significantly related to the change in calcium intake. 5. These modest losses could be a threat in women with lower bone mineral density, and indicate the importance of maintaining a high intake of calcium during dietary restriction.