OBJECTIVE: to analyze how the process of implementing an onco-hematology nursing service at a pediatric hospital in Rio de Janeiro took place. METHODS: a historical, qualitative study. Sources included written and oral documents, produced through semi-structured interviews, carried out between August 2022 and February 2023 with nurses who worked on implementing the service, represented by 40 minutes, nine care protocols and eight reports from the hospital's internal website. RESULTS: nursing staff reorganization and investment in professional improvement, through courses and graduate courses, culminated in the establishment of protocols, committees and nursing indicators, which enabled the implementation of a service with quality and safety. FINAL CONSIDERATIONS: the implementation of a nursing service in pediatric onco-hematology was successful and, while highlighting the importance of nursing, also delivered quality service to society, strengthening the Brazilian Health System.