We report a patient who experienced thrombotic obstruction of an Omniscience prosthesis three years after mitral valve replacement. At reoperation another Omniscience prosthesis was inserted which became thrombosed after eight months. Recurrent thrombosis of the same prosthesis in the same patient is unusual and raises the problem of which device to use when replacing a thrombosed valve. In our patient another mechanical prosthesis was inserted at second reoperation because of her young age and in the hope of reducing the risk of further thrombosis by using a valve with better flow characteristics such as a bileaflet prosthesis.