Adaptation of evidence-based interventions (EBIs) often occurs when implemented in new local contexts and settings. It is unclear, however, during which phase of implementation adaptations are most frequently made and how these changes may impact the fidelity, effectiveness, and sustainability of the EBI. Pediatric Early Warning Systems (PEWS) are EBIs for early identification of deterioration in hospitalized children with cancer. This study evaluates adaptations of PEWS made among resource-variable pediatric oncology hospitals in Latin America implementing and sustaining PEWS.