Background Timely diagnosis of pediatric sepsis remains elusive. We estimated the risk of potentially missed pediatric sepsis in US emergency departments (EDs) and determined factors associated with its occurrence. Methods In a retrospective study of linked inpatient and ED records from four states using administrative data (excluding 40% with missing identifiers), we identified children admitted with severe sepsis and/or septic shock who had at least one ED treat-and-release visit in the 7 days prior to sepsis admission. An expert panel rated the likelihood of each ED visit being related to subsequent sepsis admission. We used multivariable regression to identify associations with potentially missed sepsis. Results Of 1945 patients admitted with severe sepsis/septic shock, 158 [8.1%; 95% confidence interval (CI), 6.9%-9.4%] had potentially missed sepsis during an antecedent treat-and-release ED visit. The odds of potentially missed sepsis were lower for each additional comorbid chronic condition [odds ratio (OR), 0.86; 95% CI, 0.80-0.92] and higher in California (OR, 2.26; 95% CI, 1.34-3.82), Florida (OR, 3.33; 95% CI, 1.95-5.70), and Massachusetts (OR, 2.87; 95% CI, 1.35-6.09), compared to New York. Conclusions Administrative data can be used to screen large populations for potentially missed sepsis and identify cases that warrant detailed record review.