Rats fed an iron-deficient diet develop decreased bone mass and increased fragility. This study documents that rats fed two minerals likely to be low in American diets, calcium and iron, had dramatic changes in bone density and morphometry. Weanling male Long-Evans rats were fed a diet that was either deficient in iron (5-8 mg/kg or 89-143 micro mol/kg diet), low in calcium (1.0 g/kg Ca or 0.025 mol/kg diet) or deficient in both minerals or a control diet with adequate iron and calcium. Eight rats in each of the four groups were fed their respective diets for 5 wk. Total femur and tibia widths were decreased in all experimental groups and iron-deficient rats had decreased medullary widths compared with the other three groups. Cortical width was decreased in all experimental groups, with either the calcium-restricted group or the iron-deficient + calcium-restricted group showing the greatest impact. Both calcium restriction and iron deficiency, either singly or in combination with one another, had reduced cortical bone area. Analysis by dual-energy X-ray absorptiometry revealed a pattern of significant reductions in bone density for iron-deficient, calcium-restricted and the combination of calcium-restricted+ iron-deficient rats, respectively, as compared with controls. These data suggest that a commonly deficient trace element in American diets, iron, has a negative impact upon bone health, and this impact is exacerbated by a calcium-restricted diet.