Several neurological complications have been associated with the use of monoclonal antibodies (mAbs), and demyelinating disorders have been estimated to affect the 0.02-0.20% of treated patients. Alemtuzumab is a humanized chimeric mAbthat targets the CD52 antigen, it is currently approved for relapsed/refractory and high-risk untreated chronic lymphocytic leukemia (CLL). The major complication of alemtuzumab therapy is the increased risk of opportunistic infections secondary to the profound immunosuppression. Autoimmune diseases as Graves disease, immune thrombocytopenic purpura and Good pasture syndrome, have been reported to be associated to the treatment. In the present report, we present three CLL patients developing acute inflammatory demyelinating neuropathy during treatment with alemtuzumab. Despite the severity of the complication, all the patients showed an univocal good clinical response after treatment with intravenous immunoglobulin (IVIG). As alemtuzumab represents, nowadays, a key therapeutic option for CLL, clinicians should be aware of this rare and disabling toxicity.