A group of 20 patients with ruptures of the posterior cruciate ligament treated either by early mobilisation or by plaster immobilisation is described. The functional results bore no relationship to the degree of laxity of the ligament and 18 of the 20 patients considered that their symptoms did not warrant the discomfort and inconvenience ofreconstruction ofthe ligament. It is suggested that many patients with posterior cruciate insufficiency have a good functional result, and that the place of routine repair of such injuries should be questioned.