A 72-year-old woman had been diagnosed in 1998 as having colonic adenocarcinoma associated with lymphocytosis, and had undergone an operation. Three years later she was referred to our hospital with the chief complaint of blood stools. She again developed adenocarcinoma of the sigmoid colon. Blood chemistry showed a leukocyte count of 26,850/ml without anemia or thrombocytopenia. Bone marrow aspiration gave a nucleated cell count of 109,600/ml with 50.2% lymphocytes. Lymphocytes surface marker showed T-cell characteristics with CD4+/CD-. The serological test showed negative anti-HTLV-1 antibody and the TCRab chain was rearranged in her bone marrow aspirate. From these results she was diagnosed as having T-CLL.