Translocations involving the KMT2A (MLL) gene, located at 11q23, and two different partner genes, ELL and MLLT1, located at 19p13.1 and 19p13.3, respectively, have been reported in both acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL).1,2 However, there are limited data describing clinical and molecular differences between adult patients with t(11;19)(q23;p13.1) and those with t(11;19)(q23;p13.3). Neither the Mitelman Database of Chromosome Aberrations and Gene Fusions in Cancer3 nor large studies correlating chromosome abnormalities with clinical outcome4 distinguish the two types of t (11;19); instead they combine both into one cytogenetic group. Herein, we report the largest, to our knowledge, series of 35 adults with acute leukemia and t(11;19)(q23;p13.1) or t(11;19)(q23;p13.3) who were treated on Cancer and Leukemia Group B (CALGB)/ Alliance for Clinical Trials in Oncology (Alliance) trials. Our study is also the largest to describe the clinical features and disease outcomes of these patients as well as to provide mutational analyses, and gene- and microRNA (miR)-expression patterns, thereby providing the rationale to identify each as separate entities.