We describe an autopsy case of Kaposi's sarcoma in a patient with an increased count of suppressor T lymphocytes. This case was distinct from the acquired immunodeficiency syndrome. First, it did not have any detectable viral antibody relating to the acquired immunodeficiency syndrome. Second, the patient's blood sample showed that the ratio of CD8+ cell (suppressor/cytotoxic T lymphocyte) to all lymphocyte population was increased to 0.61, as compared with the normal value of 0.12 to 0.16; however, absolute number of CD4+ T cell (helper/inducer T lymphocyte) was not decreased (1800/mm3). Furthermore, this patient had two tumors arising from the thymus, a major organ of the immune system, although its functional activity could not be determined. Based on these findings we believe that Kaposi's sarcoma in his case developed under the immunodeficient condition associated with a predominant increase of CD8+ cells that might have an intimate relation to the thymoma.