The survival of 66 patients with retransplanted kidneys, from August 1963 to March 1973, was evaluated. The life expectancy after retransplantation is less than that after primary transplantation but the difference is mainly due to an increased early postoperative mortality. The prognosis after retransplantation is greatly improved if the second kidney is from a related donor. The prognosis is likewise improved if a longer period of time has elapsed between the two transplantations. Surprisingly, previous exposure to specific HL-A antigens does not worsen the prognosis for a subsequent transplanted kidney.