The posterior approach for open reduction of supracondylar fractures of the humerus has been condemned for causing decreased elbow movement. This study investigates this by comparing the range of movement in children treated by posterior open reduction and Kirschner wiring with those treated by closed reduction and immobilization. A total of 65 children with severely displaced supracondylar humeral fractures have been reviewed. There was some loss of movement in 66 per cent of the open reduction group and 42 per cent of the closed reduction group. The proportion losing more than 10 degrees of movement was the same in both groups. The difference between the two groups was due to the increased numbers in the open reduction group who lost less than 10 degrees of motion. Posterior open reduction of childhood supracondylar fractures is not associated with an important loss of elbow movement and need not be avoided on this account.