Gemtuzumab ozogamicin (GO) is an antibody-targeted chemotherapeutic agent consisting of calicheamicin, a potent cytotoxic antibiotic linked to a recombinant humanized anti CD33 monoclonal antibody directed against the CD33 antigen present on leukemic myeloblasts in most patients with acute myeloid leukemia (AML). GO is indicated for the treatment of patients with CD33 positive AML in first relapse who are 60 years of age or older and who are not considered candidates for cytotoxic chemotherapy. GO has shown moderate activity as a single agent in patients with CD33-positive refractory or relapsed acute myeloid leukaemia, with more promising results in acute promyelocytic leukaemia. The side effect profile may be an improvement on conventional chemotherapy, except for a higher frequency of veno-occlusive disease or sinusoidal obstructive syndrome, especially after a subsequent haematopoietic stem cell transplantation. Because of the different mechanisms of action and non-overlapping toxicities, the integration of this immunoconjugate with standard chemotherapy is a rational approach.