The 11q23 abnormalities are frequent cytogenetic abnormalities found in some adult and pediatric cases of primary acute leukemia (AL), and also in the majority of patients with secondary AL after previous treatment with DNA topoisomerase II inhibitors. According to the WHO classification, AL with 11q23 abnormalities involving the Mixed- Lineage-Leukemia (MLL) gene composes one category of recurring genetic abnormalities. Over 60 chromosome partners of 11q23 have been reported to date, and 33 of the presumptive gene partners of 11q23 have been cloned and analyzed at the molecular level. 11q23/MLL abnormalities have been widely recognized as an important prognosis factor in AL. Recent studies showed that the prognosis of AL with 11q23/MLL is dependent on 11q23 fusion partner, and that the prognosis of AL with 11q23/MLL according to the 11q23 fusion partner is different between adults and children. The present article summarizes the current status of prognosis and treatment of AL with 11q23/MLL according to the fusion partner especially in adult, in which prognosis analysis has not be fully established due to a small number of cases, compared with infant cases.