Bone mineral density (BMD) at the lumbar spine, femoral neck, trochanteric region, and Ward's triangle was measured using dual-energy X-ray absorptiometry (DXA) in 118 women with osteoporotic vertebral collapse (average age 65 years), divided into four groups according to numbers and SD of vertebral deformation below norms: group 1: -3SD deformations only; group 2: one -4SD deformation; group 3: two-four -4SD deformations; and group 4: 5 or more -4SD deformations. There were no significant differences between the groups. Results were compared with those from 80 premenopausal (average age 32 years, range 20-40 years) and 109 postmenopausal normal women (average age 64, range 60-70 years). Mean BMD in osteoporotic group 1 was lower than premenopausal normal women by 32% at the lumbar spine, 31% femoral neck, 30% trochanteric region, and 44% at Ward's triangle, and postmenopausal controls by 17% lumbar spine, 16% femoral neck, 17% trochanter, and 14% Ward's triangle. There was a clear trend to reduction in mean BMD between osteoporotic groups 1 and 4 at all four measured sites with significant differences at the spine of 0.102 g/cm2 (P < 0.01) and Ward's triangle 0.059 g/cm2 (P < 0.01). When compared with premenopausal controls, there was a reduction in mean BMD between osteoporotic groups 1 and 4 of 10% at the lumbar spine, 7% femoral neck, 8% trochanteric region, and 13% Ward's triangle. Receiver operating characteristic analysis showed no significant differences in diagnostic sensitivities among the four measured sites for vertebral fractures. We conclude from this cross-sectional data that the majority of bone loss in spinal osteoporosis occurs before the onset of fractures.