Whereas there is clear evidence for a strong influence of bone quantity (i.e., bone mass or bone mineral density) on vertebral mechanical behavior, there are fewer data addressing the relative influence of cortical and trabecular bone microarchitecture. The aim of this study was to determine the relative contributions of bone mass, trabecular microarchitecture, and cortical thickness and curvature to the mechanical behavior of human lumbar vertebrae. Thirty-one L3 vertebrae (16 men, 15 women, aged 75 +/- 10 years and 76 +/- 10 years, respectively) were obtained. Bone mineral density (BMD) of the vertebral body was assessed by lateral dual energy X-ray absorptiometry (DXA), and 3D trabecular microarchitecture and anterior cortical thickness and curvature was assessed by micro-computed tomography (microCT). Then compressive stiffness, work to failure, and failure load were measured on the whole vertebral body. BMD was correlated with compressive stiffness (r = 0.60), failure load (r = 0.70), and work to failure (r = 0.55). Except for the degree of anisotropy, all trabecular and cortical parameters were correlated with mechanical behavior (r = 0.36 to 0.58, p = .05 to .001, and r = 0.36 to 0.61, p = .05 to .0001, respectively). Stepwise and multiple regression analyses indicated that the best predictor of (1) failure load was the combination of BMD, structural model index (SMI), and trabecular thickness (Tb.Th) (R = 0.80), (2) stiffness was the combination of BMD, Tb.Th, and curvature of the anterior cortex (R = 0.82), and (3) work to failure was the combination of anterior cortical thickness and BMD (R = 0.68). Our data imply that measurements of cortical thickness and curvature may enhance prediction of vertebral fragility and that therapies that improve both vertebral cortical and trabecular bone properties may provide a greater reduction in fracture risk.