The rupture of the medial collateral ligament of the knee joint due to sports injuries is the most common lesion of ligaments of the knee in athletes. The treatment is usually non-operative. We compared in a retrospective study the conservative treatment of these ruptures by two different methods. One group of patients was immobilised in a plaster cast for six weeks, one group of patients was partially immobilised with a brace, initiating early functional therapy. The results proved that the group of early mobilisation was significantly better in late results, in shorter rehabilitation and in all other aspects regarded as important for the treatment of such an injury. Therefore we feel the treatment with plaster casting for isolated ruptures of medial collateral ligaments as the knee should be abandoned.