Bosutinib (BOSULIF®), an orally administered BCR–ABL tyrosine kinase inhibitor (TKI) developed by Pfizer Inc., is well established in the EU and the USA as a treatment for adults with newly diagnosed (ND) chronic phase (CP) Philadelphia chromosome-positive (Ph+) chronic myelogenous leukemia (CML), and for CP, accelerated phase and blast phase Ph+ CML that is resistant or intolerant (R/I) to prior therapy. In September 2023, based on clinical data from patients aged ≥ 1 to < 18 years, bosutinib was approved in the USA for the Query ID="Q2" Text="Kindly check and confirm the processed article note" treatment of pediatric patients aged ≥ 1 year with CP Ph+ CML that is ND or R/I to prior therapy. This article summarizes the milestones in the development of bosutinib leading to this first pediatric approval.