Mycosis fungoides is the most common form of cutaneous T-cell lymphomas. The related Sezary syndrome is a more aggressive form in which the skin is diffusely affected and the peripheral blood is involved. Although easily managed during its early phases, late-stage mycosis fungoides/Sezary syndrome is usually difficult to treat and becomes refractory to chemotherapy. Recently, promising case-based results have been obtained with alemtuzumab, a humanized immunoglobulin G1 monoclonal antibody that binds to CD52 cell surface antigens, in the treatment of advanced stage mycosis fungoides/Sezary syndrome. We report a case of Sezary syndrome treated successfully with alemtuzumab but who died of treatment-related infection.