To identify risk factors of high flow nasal cannula (HFNC) failure at a US pediatric hospital without a co-located ICU. Retrospective cohort study of patients aged 0 to 18 years who were started on HFNC in the emergency department or inpatient unit at a community hospital over a 16-month period. Children with chronic medical conditions were excluded. Outcome was HFNC failure, defined as HFNC need greater than floor limit, noninvasive positive pressure, or mechanical ventilation. In bivariate analysis, we compared demographic and clinical factors between those with and without failure. We included variables in a multivariable model on the basis of statistical significance. We used Poisson regression with robust error variance to calculate the adjusted relative risk (aRR) of failure for each variable. Of 195 children, 51% had HFNC failure. In adjusted analysis, failure was higher in all age groups <12 months as compared with older children. For example, children aged 3 to 5 months had a higher risk of failure compared with patients 12 months or older (aRR 1.85, confidence interval [CI] 1.34-2.54). Patients with an asthma exacerbation had a higher risk of failure (aRR 1.39, CI 1.03-1.88). Patients whose respiratory rate or heart rate did not improve also had a higher risk of failure (aRR 1.73, CI 1.24-2.41; aRR 1.47, CI 1.14-1.90). Patients who were younger, had asthma, and did not have improved respiratory rate or heart rate after HFNC were more likely to experience HFNC failure.