In the present study, the fixation system of a femoral medullary nail connection was investigated. In surgical treatment of fractured femurs, the fracture is bridged by a medullary nail that is fixed by interlocking screws in the bone. Bone failure around these screws is the most common complication associated with the treatment of fractures of osteoporotic bone. The present study analyses the stresses present in the region of the implant/bone system. Three-dimensional finite element models were generated, a nonlinear structure analysis performed, and the stresses at material interfaces investigated. The highest concentration of stresses is to be found in the middle of the interlocking screws and the holes drilled in the bone. This is in agreement with the results of experimental investigations.