A 59-year-old man was admitted to our hospital because of disturbance of consciousness and hyponatremia. The patient had suffered from acute myelogenous leukemia (AML) with 46,XY and received chemotherapy for 5 years. Meningeal carcinomatosis was diagnosed due to the detection of carcinoma cells in the cerebrospinal fluid (CSF). Hyponatremia was caused by syndrome of inappropriate secretion of anti-diuretic hormone (SIADH). Bone marrow examination revealed myelodysplastic syndrome (MDS) with deletion of the long arm of chromosome 7. Emergence of a new abnormal clone was suggested. The patient died from brain herniation. Post mortem examination showed adenocarcinoma in the colon. An association between chemotherapy and both colon cancer and MDS was suggested.