Pediatric acute lymphoblastic leukemia (ALL) is a heterogeneous disease. At the German Cancer Congress 2016, held in Berlin, Germany, from 24 to 27 February 2016, Martin Schrappe, MD, PhD, from University Medical Center Schleswig-Holstein, Campus Kiel, Kiel, Germany, explains that there have been significant advances in the understanding of pediatric ALL subtypes and there is now a need to define the clinical importance of these subtypes.