Twenty-seven patients received the anti-CD52 monoclonal antibody alemtuzumab for hematologic malignancies and autoimmune cytopenias in a tuberculosis-endemic area. Seven patients developed mycobacterium tuberculosis (TB) infections (median: 4, 1-24, months from alemtuzumab). The actuarial 1- and 2-year incidence of TB was 31% and 45%. All patients had severe depression of lymphocyte counts subsequent to alemtuzumab treatment, and tuberculosis was extra-pulmonary in three cases. All seven patients had received prior chemotherapy/immunosuppression and tuberculosis had not occurred until alemtuzumab was administered. Patients receiving alemtuzumab in areas endemic for tuberculosis should have careful initial evaluation of TB exposure, so that prophylactic antibiotics might be administered. Tuberculosis reactivation should be considered for unexplained fever and symptoms after alemtuzumab treatment.