Over a 3-year period, we have treated 10 delayed unions of the tibia by using percutaneous marrow injection rather than standard operative bone grafting. Nine of the 10 fractures responded by forming callus in the area where the marrow was injected. This relatively simple technique avoided potential problems associated with operative grafting methods that have been standard for at least 50 years. Most importantly, it encourages early treatment of fractures when healing problems are anticipated or are becoming evident.