OBJECTIVE: There are many classification systems for injuries of the thoracolumbar spine. The recent Thoracolumbar Injury Classification and Severity Score (TLICS) has been shown to be a reliable tool for adult patients. The aim of this study was to assess the reliability of the TLICS system in pediatric patients. The validity of the TLICS system is assessed in a companion paper. METHODS: The medical records of pediatric patients with acute, traumatic thoracolumbar fractures at a single Level 1 trauma center were retrospectively reviewed. A TLICS was calculated for each patient using CT and MRI, along with the neurological examination recorded in the patient's medical record. TLICSs were compared with the type of treatment received. Five raters scored all patients separately to assess interrater reliability. RESULTS: TLICS calculations were completed for 81 patients. The mean patient age was 10.9 years. Girls represented 51.8% of the study population, and 80% of the study patients were white. The most common mechanisms of injury were motor vehicle accidents (60.5%), falls (17.3%), and all-terrain vehicle accidents (8.6%). The mean TLICS was 3.7 ± 2.8. Surgery was the treatment of choice for 33.3% of patients. The agreement between the TLICS-suggested treatment and the actual treatment received was statistically significant (p < 0.0001). The interrater reliability of the TLICS system ranged from moderate to very good, with a Fleiss' generalized kappa (k) value of 0.69 for the TLICS treatment suggestion among all patients; however, interrater reliability decreased when MRI was used to contribute to the TLICS. The k value decreased from 0.73 to 0.57 for patients with CT only vs patients with CT/MRI or MRI only, respectively (p < 0.0001). Furthermore, the agreement between suggested treatment and actual treatment was worse when MRI was used as part of injury assessment. CONCLUSIONS: The TLICS system demonstrates good interrater reliability among physicians assessing thoracolumbar fracture treatment in pediatric patients. Physicians should be cautious when using MRI to aid in the surgical decision-making process.