Medial collateral ligament (MCL) sprains are tension injuries to the medial ligamentous structures of the knee. They are usually the result of an acute blow to the lateral aspect of the knee. The diagnosis can usually be made on the basis of a characteristic clinical examination. The treatment of these injuries has evolved over several years. Current recommended treatment for isolated MCL sprains is lightweight support and an aggressive early functional rehabilitation programme. In combined injuries, cruciate ligaments are usually surgically reconstructed and the MCL treated non-operatively. Although many braces have been developed to prevent MCL sprains, their effectiveness is uncertain.