Two cases of necrotizing myelopathy were autopsied; one was complicated with lung carcinoma and the other with chronic type adult T cell leukemia (ATL leukemia). To our knowledge, they were the first cases of their type in Japan. In both cases, necrosis of the spinal cord was observed in the gray and white matter along most of its extent. Marked changes were found in the lumbar segment. The patients were not treated with intravenous cancer chemotherapy or irradiation. Immunohistochemical and electron microscopic examination revealed an extremely strong infection of herpes simplex virus (HSV) type 2. However, HSV type 1 and cytomegalovirus antigens were not detected.