Résumé : RATIONALE AND OBJECTIVES. The accuracy of the measurement of the size of cortical bone on computed tomography (CT) images of human vertebrae was evaluated using an automated contour detection and segmentation procedure. METHODS. Forty human lumbar vertebrae were scanned using 8-mm slices and an automated detection for definition of trabecular and cortical region of interest. The vertebrae were embedded in a polyester resin and 8-mm-thick midvertebral specimens were excised using a diamond circular saw. Contact radiographs of these specimens were performed and, after photograph magnification, the cortical area was measured using computerized planimetry. RESULTS. Cortical area measured on CT images was highly correlated with the area measured by planimetry on the specimens (r =.91; P <.001) with, however, a systematic overestimation. A significant relationship was found between density and width of the cortex (r =.56; P <.001). CONCLUSIONS. Computed tomography is able to assess the size of cortical bone in human vertebrae, but a threshold detection algorithm, as used in the current study, is not adequate to obtain the precise anatomic dimensions. © 1993, J.B. Lippincott Company.