Background: Malnutrition during cancer treatment increases treatment-related morbidity and mortality. Our study better characterizes variability in malnutrition identification and treatment by examining nutrition-related diagnoses and support for children with central nervous system (CNS) and non-CNS solid tumors during therapy. We examined diagnosis of malnutrition, use of tube feeding or parenteral nutrition (PN), and appetite stimulants.Methods: We retrospectively reviewed 0 to 21-year-old patients in the Pediatric Health Information System from 2015 to 2019. Patients were classified as having (1) billed malnutrition diagnosis, (2) malnutrition diagnosis or using PN and enteral nutrition ("functional malnutrition"), and (3) any previous criteria or prescribed appetite stimulants ("possible malnutrition"), as well as associated risk factors.Results: Among 13,375 unique patients, CNS tumors were most common (24.4%).Overall, 26.5% of patients had malnutrition diagnoses, 45.4% met functional malnutrition criteria, and 56.0% had possible malnutrition. Patients with adrenal tumors had highest billed, functional, and possible malnutrition (36.6%, 64.1%, and 69.4%, respectively) followed by CNS tumors (29.1%, 52.4%, and 64.1%). Patients with adrenal tumors had highest rates of PN use (47.4%) and those with CNS tumors had the highest tube feeding use (26.8%). Hospital admissions with malnutrition had a longer hospital length of stay (LOS) (6 vs 3 days, P < 0.0001), more emergency department admissions (24.4% vs 21.8%, P < 0.0001), and more opioid use (58.6% vs 41.4%, P < 0.0001).Conclusions: Variability in malnutrition diagnoses hinders clinical care and nutrition research in pediatric oncology. Improving disease-specific recognition and treatment of malnutrition can target nutrition support, ensure appropriate reimbursement, and potentially improve outcomes for children with solid tumors.