A rare neoplasm, disseminated visceral Kaposi's sarcoma, appeared rapidly during the late rejection of a homograft kidney in a 35-year-old Negro woman. No evidence of tumor was present in the recipient prior to transplantation, and postmortem examination of the donor also revealed no neoplasia. Some features of Kaposi's sarcoma suggest its similarity to neoplasms of the Burkitt's type. It appears possible that immunosuppressant therapy may have permitted the development of this tumor in a transplant recipient.