The present study was intended to examine the efficacy and safety of bendamustine monotherapy in patients with previously untreated chronic lymphocytic leukemia (CLL) for whom treatment with fludarabine (FLU) was not suitable, and in FLU-na < ve patients with relapsed/refractory CLL. We intravenously administered bendamustine 100 mg/m(2)/day on days 1 and 2 of each 28-day cycle to 10 patients (eight previously untreated; two relapsed/refractory) up to six cycles. The primary endpoint was overall response rate (ORR: partial remission or better) according to the 2008 International Workshop on the CLL guidelines. The ORR was 60.0% (6/10), with the 95% confidence interval of 26.2-87.8%. Neither disease progression nor mortality occurred during follow-up. Therefore, the medians for progression-free survival, duration of response, and overall survival were estimated to exceed 12.6, 8.7, and 12.6 months, respectively. Adverse events (AEs) occurred in all 10 patients. Grade 3/4 hematologic AEs included lymphopenia (90%), neutropenia (80%), CD4 lymphopenia (80%), and leukopenia (70%). Nonhematologic AEs included constipation (80%), nausea (80%), malaise (50%), and anorexia (50%). There was one case each of grade 3 infection and adenocarcinoma of the stomach. Bendamustine showed high efficacy for Japanese patients with previously untreated or relapsed/refractory CLL, and its safety profile was acceptable.