The new community laws regarding medical devices require that custom-made devices be prescribed by the surgeon, who assumes responsibility for the device along with the manufacturer. It is the purpose of this study to indicate a method that allows use to check whether custom-made prostheses in particular conform to the requirements established by European laws; these are prostheses produced in a single model and that have rather short development and realization times. The pre-clinical method of validation proposed, based on a calculation with finite elements, was first verified by in vitro measurements and then used to evaluate 15 cases selected among the most critical ones in terms of size and/or geometrical irregularity from a group of 100 stems that had already been implanted. The method proposed was confirmed to be accurate and reliable; in 3 out of 15 stems analyzed we found values for mechanical resistance that were less than minimum values required by law.