Michael J BurkeDepartment of Pediatrics, Division of Hematology/Oncology/Bone Marrow Transplantation, Medical College of Wisconsin, Milwaukee, WI, USAAbstract: Using targeted therapy for treatment of cancer has become the paradigm to which clinical trials aspire. Imatinib, the BCR-ABL1 tyrosine kinase inhibitor (TKI), was the first of its kind to specifically target and inhibit the underlying Philadelphia chromosome (Ph+) oncogene found to be driving chronic myeloid leukemia in adults, and has since become standard of care for the treatment of chronic myeloid leukemia in children. Imatinib, with its ability to target Ph+ leukemia, has been successfully incorporated into the treatment of not only pediatric chronic myeloid leukemia but also Ph+ acute lymphoblastic leukemia. With the incorporation of imatinib into combination chemotherapy for pediatric Ph+ acute lymphoblastic leukemia, current survival rates are far higher than at any other time for this once dreadful disease. With more children today receiving treatment with imatinib for either chronic myeloid leukemia or Ph+ acute lymphoblastic leukemia, knowledge is accumulating surrounding the short-term and long-term toxicities observed in children, adolescents, and young adults treated with this TKI. In summary, the TKI imatinib has made a historic impact in the treatment of pediatric Ph+ leukemias, transforming what were once very high-risk diseases with considerable morbidity and mortality into ones that are now very treatable but with a new awareness surrounding the long-term toxicities that may come with this price for cure.Keywords: imatinib, leukemia, lymphoblastic leukemia, chronic myeloid leukemia, pediatric