We conducted a double-blind, placebo-controlled, randomized trial to determine whether 1 year of supplemental calcium intake would augment hip [greater trochanter, GT, femoral neck (FN), total hip (TH)], spine (LS), and femoral mid-shaft (Fmr) BMD in female distance runners. Twenty-three women (age: 23.7 +/- 4.7 yrs, height: 165.6 +/- 6.3 cm, weight: 55.7 +/- 6.1 kg) were randomly assigned to receive either 1000 mg/d of supplemental calcium (N = 13) or placebo tablets (N = 10) for 1 year. BMD was determined by DXA (Hologic 1000-W) and tablet compliance by self-report logs. Compliance averaged 79% and 71% for supplement and placebo groups, respectively. Calcium supplementation did not affect hip or spine BMD, but did prevent loss at the femoral mid-shaft (GT: -0.5% vs. 0.2%, FN: 0.9% vs. 1.1%, TH: -0.3% vs. 0.2%, LS: 0.3% vs. 1.2%, Fmr: 0.1% vs. -1.8%, for calcium vs. placebo, respectively). We conclude that the addition of 800 mg/d of supplemental calcium to the diet of young adult female distance runners with habitual calcium intakes of approximately 1000 mg/d, prevents cortical but not trabecular bone loss.