In the early years, mortality rates for pediatric hematopoietic cell transplant (HCT) patients with critical illness were abysmal, exceeding 80%. This led to the general belief that providing critical care resources to this population was futile (1). Volume I of this Research Topic published 30 articles from 211 authors in 9 different countries (2). In this first volume, Pechlaner et al. reported a PICU mortality of 11% for pediatric hematology/ oncology patients (3)a significant improvement from the early years. This volume extensively discussed management of complications from HCT, cancer, and chimeric antigen receptor therapy (CAR-T) (4-6). Management of these complications involved utilization of critical care resources such as continuous renal replacement therapy (CRRT) (7), extracorporeal membrane oxygenation (ECMO) (8), and mechanical ventilation (9)resources that would not have been considered for this population in the early years.Improvement in outcomes may be partially explained by topics discussed in this first volume. These include 1) utilization of strategies to promote early recognition of clinical deterioration leading to earlier interventions and involvement of critical care teams (5, 9-13); 2) use of invasive diagnostic procedures such as bronchial alveolar lavage and lung biopsy which may lead to more accurate diagnoses and targeted therapies (14, 15); and 3) careful attention to detail such as prevention of the detrimental effects of fluid overload (16).In the current Research Topic, Critical Complications in Pediatric Oncology and Hematopoietic Cell Transplant, Volume II, there is a continuation of the themes of improving outcomes and strengthening collaboration. This Research Topic contains 21 publications from 195 authors representing 22 different countries on 5 continents Frontiers in Oncology frontiersin.org 01