Background: When patients are transported by EMS and later require subsequent transfer to another facility (secondary transport), patient care is compromised and healthcare resources wasted. Previously, the rate of secondary transport has been estimated indirectly. Using the Maryland’s comprehensive all-payers dataset for hospital based care (ED and inpatient) and comprehensive EMS dataset, we sought to directly measure secondary transport in pediatrics. Objective: To determine the proportion of children transported by EMS who require secondary transport from the primary destination ED. To determine relative frequency of conditions seen in children who are discharged from the primary ED, transferred out from the primary ED and admitted to the same or a secondary hospital after ED evaluation. Methods: We linked comprehensive state level datasets from Maryland from 2015-2016, including EMS records for all children (age < 18 years) transported by 911 EMS for all emergency department (ED) and inpatient (IP) visits. ED and inpatient records were linked to EMS records using probabilistic linkages (PL) based on seven elements: date of service, gender, patient age, date of birth, zip-code, county, and destination hospital. Results: Pediatric patients transported by 911 to Maryland hospitals comprised 66,373 eligible EMS records, 823,960 ED records and 176,579 IP records. Using PL strategy, 61,014 (92%) of EMS records were linked to one or more ED/IP dataset records. 52,567 patients (79%) were treated and discharged by the EMS destination ED while 3,605 (5.9%) were admitted from the destination ED to inpatient unit at the same hospital. 3,653 (6%) were transferred from the destination ED to another facility (secondary transport). The most common diagnoses associated with secondary transport were seizure (17.8%), asthma (5.9%), and upper limb fracture (5.8%). Table 1 lists the odds of secondary transport for several common diagnoses. Conclusions: The majority of pediatric patients transported by EMS are discharged home from the primary destination ED. However, when EMS transported patients are not discharged from the ED, approximately half require transport to another facility for care. These findings should be combined with more granular data to develop evidence based decision support to guide EMS destination choice for pediatric patients and reduce secondary transport.