Summary 136 patients underwent mitral-valve replacement with the Björk-Shiley disc valve. The overall postoperative mortality was 9.5%. There have been no deaths in the last group of 55 patients. This improvement is primarily due to the improvements in surgical technique and postoperative intensive care. After a mean observation time of 16 months, the late results on the 123 survivers showed that the Björk-Shiley disc valve, with its central flow, gives better results than ball valves or autogenous-tissue valves.