Does weight-bearing exercise offset bone loss associated with oligomenorrhea? If so, bone mineral density (BMD) will be stable at weight bearing sites but decrease at non-weight-bearing sites with increasing duration of oligomenorrhea. To test this hypothesis, BMD (g/cm2), was measured by dual-energy X-ray absorptiometry in 41 oligomenorrheic ballet dancers aged 17.7 +/- 0.2 years (mean +/- SEM) and 46 age-matched controls with normal menstrual function. BMD correlated negatively with the duration of oligomenorrhea at weight-bearing and non-weight-bearing sites (femoral neck, r = -0.33, p < 0.05; Ward's triangle, r = -0.29, p = 0.06; trochanter, r = -0.33, p < 0.05; lumber spine, r = -0.25, p = 0.1; skull, r = -0.29, p = 0.06; arms, r = -0.32, p < 0.05; ribs, r = -0.30, p = 0.06). The slopes of the regression of BMD on duration of oligomenorrhea were greater at the proximal femur (trochanter, -0.28 +/- 0.13, femoral neck, -0.24 +/- 0.11; Ward's triangle, -0.29 +/- 0.15) than the skull (-0.15 +/- 0.08, p < 0.05, p < 0.1, p < 0.1 respectively). The slopes at the trochanter and femoral neck were also greater than at the ribs (-0.10 +/- 0.05; both p < 0.1). In the dancers with oligomenorrhea of less than 40 months duration, BMD was higher than the age-predicted mean at weight-bearing sites (except the lumber spine), but not at non-weight-bearing sites (femoral neck, 9.1 +/- 3.4%; Ward's triangle, 10.0 +/- 1.7%; trochanter, 9.4 +/- 4.1%, all p < 0.05; lumbar spine, -2.1 +/- 2.7%, NS; skull, -2.5 +/- 2.1%, NS; ribs, -3.0 +/- 1.6% NS; arms, -3.9 +/- 1.6%; p < 0.05). In the dancers with greater than 40 months oligomenorrhea, BMD was no higher than the age predicted mean, at the weight bearing sites, and was lower at non-weight bearing sites (femoral neck, 4.3 +/- 2.3%, NS; Ward's triangle, 3.5 +/- 3.2%, NS; trochanter, 2.1 +/- 2.7%, NS; lumbar spine, -3.8 +/- 2.1%, NS; arms, -7.5 +/- 0.8%, p < 0.05; skull, -6.2 +/- 1.8%, p < 0.01; ribs, -5.4 +/- 1.1%, p < 0.0001). In conclusion, weight-bearing exercise is unlikely to offset the deleterious effects of oligomenorrhea. Bone loss appears to occur at all sites but may begin from a higher level at weight-bearing sites and may proceed more rapidly.