This study used clinical quantitative computer tomography (QCT) to obtain detailed estimates of the structural properties and cortical dimensions of cross-sections (CSs) along the femoral neck (FN). The computer tomography scans of both proximal femora of 27 postmenopausal women (mean age 81, range 65-86yr) with osteoporosis were processed and analyzed. The cross-sectional shape, cortical and trabecular bone area, and section moduli under different fall directions were calculated. Furthermore, each CS was divided into 8 sectors and cortical thickness and buckling ratio were estimated for each octant. The cross-sectional shape was found to be increasingly elliptic and both tensile and compressive section moduli increased significantly (by a factor of up to 1.8) from the proximal to distal half of the FN. The section modulus was dependent on the fall direction; it was maximal when falling 20 degrees anterior and at its lowest (reduced by as much as 37%) when falling 50 degrees posterior on the greater trochanter. The cortex was significantly thinner (< or =1mm) in the anterior, superoanterior, superior, superoposterior, and posterior octants than the inferomedial aspect of the FN. In conclusion, multiple site measurements are required for a comprehensive assessment of FN structural properties, which can be studied based on clinical QCT.