Rearrangements of the MLL gene located at 11q23 are common chromosomal abnormalities associated with acute leukemia (AL), especially infant and secondary leukemia after previous treatment with DNA topoisomerase II inhibitors. 11q23/MLL abnormalities have been widely recognized as an important prognostic factor in AL. Over 70 chromosome partners of 11q23 have been identified to date, at least 50 of which have been cloned and characterized at the molecular level. Recent studies showed that the prognosis of 11q23/MLL AL varies widely according to the partner gene, the leukemia cell lineage, the age of the patient and the treatment administered. Special strategies are needed to treat 11q23/MLL AL, including allogeneic hematopoietic stem cell transplantation, according to the fusion partner. The development of novel methodologies, including new molecular therapeutic targets, is also needed to improve the prognosis of 11q23/MLL AL. The present article provides an update on the current status of prognosis and treatment of 11q23/MLL AL according to the fusion partner.