A prospective study was carried out on 142 fresh fractures of the tibial shaft treated by internal fixation according to the AO principles, 99 fractures being closed and 43 open. A total of 140 cases was reviewed at 1 year and 125 cases at 2 years following injury, at which times a functional assessment score was awarded by the surgeon and the patient himself, and a precise measurement of ankle range was made. The time taken for the fracture to unite and the incidence of non-union was greater if the fracture was comminuted (whether open or closed) than if there was no comminution. For patients with closed fractures the minor infection rate (erythema and increased local temperature) was 4.1 per cent and the major infection rate (pus present) was 4.1 per cent, no infection being severe enough to warrant removal of the plate. In open fractures, the overall infection rate was 14 per cent, 7 per cent having major infection and only 1 case requiring removal of the plate. The functional results and complications are discussed.