Variation in patient care or outcomes may indicate an opportunity to improve quality of care. We evaluated the variation in testing, treatment, hospitalization rates, and outcomes of febrile young infants in US pediatric emergency departments (EDs). Retrospective cohort study of infants <90 days of age with a diagnosis code of fever who were evaluated in 1 of 37 pediatric EDs between July 1, 2011 and June 30, 2013. We assessed patient- and hospital-level variation in testing, treatment, and disposition for patients in 3 distinct age groups: ≤28, 29 to 56, and 57 to 89 days. We also compared interhospital variation for 3-day revisits and revisits resulting in hospitalization. We identified 35,070 ED visits that met inclusion criteria. The proportion of patients who underwent comprehensive evaluation, defined as urine, serum, and cerebrospinal fluid testing, decreased with increasing patient age: 72.0% (95% confidence interval [CI], 71.0-73.0) of neonates ≤28 days, 49.0% (95% CI, 48.2-49.8) of infants 29 to 56 days, and 13.1% (95% CI, 12.5-13.6) of infants 57 to 89 days. Significant interhospital variation was demonstrated in testing, treatment, and hospitalization rates overall and across all 3 age groups, with little interhospital variation in outcomes. Hospitalization rate in the overall cohort did not correlate with 3-day revisits (R(2) = 0.10, P = .06) or revisits resulting in hospitalization (R(2) = 0.08, P = .09). Substantial patient- and hospital-level variation was observed in the ED management of the febrile young infant, without concomitant differences in outcomes. Strategies to understand and address the modifiable sources of variation are needed.