Eleven patients with severe corneal disease have been operated with a collar-button-shaped keratoprosthesis and have been followed for 9-36 months. Two of the devices have been removed, but the remainder are securely in place. Six of the patients have benefitted substantially in terms of improved vision. The complications have been reviewed, and some factors for success have been identified. Thus, to keep the keratoprosthesis temporarily buried beneath tissue (conjunctiva or skin), application of collagenase-suppressing medication and reduction of evaporative damage to the wound around the device seem particularly important.