Fifty non-unions of the tibia that were present in forty-nine patients after external fixation and immobilization in a cast for a high-energy fracture were subsequently treated by compression plating. Initially, there were forty-six open fractures and four closed fractures with a compartment syndrome. Twenty-two non-unions (44 per cent) had early soft-tissue reconstruction (thirteen rotational and nine free flaps). The duration of external fixation averaged ten weeks, and the mean time from injury to plating was eight months. None of the non-unions were infected at the time of plating. The average preoperative deformity in the sagittal (anterior-posterior) plane was 8 degrees and in the frontal (medial-lateral) plane, 9 degrees; after plate fixation, the residual angulation averaged 3 and 2 degrees. Autogenous bone graft was used in thirty-nine of the fifty non-unions. The patients were followed for an average of twenty-four months. Forty-six (92 per cent) of the non-unions united, in an average of seven months, without further intervention. In four patients (8 per cent), the plate broke, necessitating re-plating in three and external fixation in one (the latter patient had an infected non-union). A deep infection developed in three patients (6 per cent). Ultimately, forty-eight non-unions (96 per cent) healed without evidence of infection. Plate osteosynthesis is an effective method of treatment for patients who have had an open fracture of the tibia that has failed to unite after external fixation and immobilization in a cast.