In the field of uncemented hip arthroplasties, secondary biologic fixation of femoral implants depends directly on the quality of the primary stability. Metaphyseal filling and a good fit between the implant and the proximal femur improve initial stabilization and optimize the transmission of forces to the bone. Precise knowledge of the three-dimensional femoral shape is essential to the design and selection of adapted implants. Three hundred ten femurs in 300 patients suffering from primary hip osteoarthritis were analyzed by computed tomography scanning. After three-dimensional reconstruction, several measurements were extracted, and the parameters essential to the characterization of the diverse femoral morphologies encountered were identified. A new classification of the proximal femur is proposed. The consequences on the design and the preoperative selection of femoral implants are discussed.