It was the aim of this study to record quantitatively and qualitatively the distribution of the three-dimensional microarchitecture throughout the human spine in osteoporosis. Bone biopsies of the iliac crest and the complete spine of 26 autopsy cases without skeletal disease and 11 female patients with proven osteoporosis were removed. Grindings of all vertebrae by a technique which we developed allowed two- and three-dimensional measurements simultaneously. The analysis included an evaluation of trabecular bone volume, trabecular interconnection, and trabecular thickness, as well as a qualitative investigation of the structure of cancellous bone. The bone loss in osteoporosis is a loss of structure. The relative loss of the trabecular microarchitecture is greater in the iliac crest than in the lumbar spine. It is a gradual change from normal bone to osteoporosis. Transformation from plates to rods and the loss of whole trabeculae are caused by perforations. The polyostotic heterogeneity in osteoporosis is remarkable. Adjacent vertebrae may show differences of up to 100% in bone structure and bone volume. This explains the difficulties in early diagnosis of osteoporosis. Due to the polyostotic heterogeneity it is impossible to define a threshold mineral content for osteoporotic fractures.