Introduction: Patient reported outcome (PRO) measures correlate with heart failure (HF) severity among adults and are widely used as adjunct tools in the assessment of adult HF. However, limited data exist in pediatric HF. PROs may be valuable in monitoring heart failure (HF) status in children. Hypothesis: Patient Reported Outcome Measurement Information System (PROMIS) fatigue score correlates with HF severity in children. Methods: In this prospective cohort study, English and Spanish speaking patients were recruited from 4 pediatric HF centers 09/2019 - 02/2023. Children 8.0 to 18.0 years old with systolic and/or diastolic HF were enrolled while receiving inpatient HF treatment. Pediatric self-report PROMIS measures were administered during inpatient treatment and at additional outpatient follow-up time point(s) within 6 months post-discharge. Measures included mobility, fatigue, anxiety, depressive symptoms, and peer relationships. NYU HF Index scores were calculated at each time point. Pearson’s correlation with a 95% confidence interval (CI) compared PROMIS Fatigue T-score and NYU HF Index score at the inpatient time point, and a linear mixed effects model determined their association over time. Results: We enrolled 41 patients with median age of 13.5 ±4.2 years. Patient diagnoses included cardiomyopathy (48.8%), congenital heart disease (41.5%) and other (9.7%). Twenty patients (48.8%) were discharged from hospital alive and without a VAD or heart transplant, of which 18 completed both inpatient and outpatient follow-up assessment. Median PROMIS Fatigue T-scores and NYU HF Index scores improved from inpatient to outpatient assessment. NYU Index scores improved from 12.0 (IQR 11.2, 15.0) to 7.5 (IQR 5.8,10.2); p<0.05. PROMIS fatigue scores improved from 58.5 (IQR 54.6, 64.9) to 50.2 (IQR 33.5, 59.2); p<0.05. The correlation between PROMIS Fatigue T-score and NYU HF Index score at the inpatient time point was 0.5 (95% CI 0.2, 0.7), and their correlation over time was 0.5 (95% CI 0.3, 0.6). Conclusions: PROMIS Fatigue T-score moderately correlates with HF severity in children. Larger scale application of PROMIS could aid in longitudinal symptom management of pediatric HF patients and should be further tested in routine clinical care.