Resistance to fracture depends not only on the total amount of trabecular bone but also on the size and distribution of the trabeculae. We used an image analysis computer to make direct measurements of trabecular width and separation in 33 normal subjects, aged 20 to 80 years. Multiple regression analysis showed that an increase in the distance between adjacent trabeculae accounted for 67.6% of the reduction in trabecular bone area in normal subjects with advancing age, with an additional 23.2% attributed to decreased trabecular width (P & lt;​ 0.001). The role of trabecular atrophy in the loss of bone with age was clearly established from the direct relationship between trabecular bone area and the independently measured trabecular width (r = 0.763, P & lt;​ 0.001). Effective treatment could increase trabecular bone by thickening the remaining trabeculae. It is, however, unlikely that treatment would replace trabeculae that have been removed or would restore biomechanical strength to the skeleton.