T-cell prolymphocytic leukemia(T-PLL)is a highly aggressive hematopoietic malignancy with poor prognosis and is extremely rare in Japan. Since T-PLL cells usually express high levels of CD52, the anti-CD52 monoclonal antibody alemtuzumab is expected to exhibit an antitumor effect via its antibody-dependent cell cytotoxicity(ADCC)and complement-dependent cytotoxicity(CDC). However, the therapeutic efficiency of alemtuzumab for T-PLL has not been established in Japan. Furthermore, only a few patients have completed the treatment schedule because of adverse events. Here, we report a 64-yearold woman with multiple comorbidities who was successfully treated with alemtuzumab.