The authors present their experience in the application of a Fixion expansion intramedullary nail for the treatment of diaphyseal fractures of the humerus and tibia, in a total of 40 surgeries. The features of the nail are: stability and flexibility of the instrumentation, speed of surgery, minimal exposure to radiation. The results obtained up to now are encouraging; there are no significant problems either during or after surgery, and mean consolidation time is 3 months for fractures of the humerus, and 4 months for those of the tibia. The Fixion nail is a versatile type of instrumentation that is easy to use.