INTRODUCTION: FAST exam has long been proven useful in the management of adult trauma patients, however, its utility in pediatric trauma patients is not as proven. Our goal was to evaluate the utility of a FAST exam in predicting the success or failure of non-operative management (NOM) of blunt liver and/or spleen (BLSI) in the pediatric trauma population. METHODS: A retrospective analysis of a prospective observational study of patients less than 18 years of age presenting with BLSI to one of ten level-1 pediatric trauma centers (PTC) between April 2013 and January 2016. 1008 patients were enrolled and 292 had a FAST exam recorded. We analyzed failure of NOM of BLSI in the pediatric trauma population. We then compared FAST exam alone or in combination with the pediatric age adjusted shock index (SIPA) as it relates to success of NOM of BLSI. RESULTS: FAST exam had a negative predictive value (NPV) of 97% and positive predictive value (PPV) of 13%. The odds ratio of failing with a positive FAST exam was 4.9 and with a negative FAST was 0.20. When combined with SIPA a positive FAST exam and SIPA had a PPV of 17%, and an odds ratio for failure of 4.9. The combination of negative FAST and SIPA had a NPV of 96% and the odds ratio for failure was 0.20. CONCLUSION: Negative FAST is predictive of successful NOM of BLSI. The addition of a positive or negative SIPA score did not affect the positive or negative predictive value significantly. FAST exam may be useful clinically in determining which patients are not at risk for failure of NOM of BLSI and do not require monitoring in an intensive care setting. LEVEL OF EVIDENCE: Level II, Prognostic Study