While most children with mild traumatic brain injury (mTBI) without intracranial injury (ICI) can be safely discharged home from the emergency department, many are admitted to the hospital. To support evidence-based practice, we developed a decision tool to help guide hospital admission decisions. This study was a secondary analysis of a prospective study conducted in 25 emergency departments. We included children under 18 years who had Glasgow Coma Scale score 13-15 head injuries and normal computed tomography scans or skull fractures without significant depression. We developed a multi-variable model that identified risk factors for extended inpatient management (EIM; defined as hospitalization for 2 or more nights) for TBI, and used this model to create a clinical risk score. Among 14,323 children with mTBI without ICI, 20% were admitted to the hospital but only 0.76% required EIM for TBI. Key risk factors for EIM included Glasgow Coma Scale score less than 15 (odds ratio [OR] = 8.1; 95% confidence interval [CI] 4.0-16.4 for 13 vs. 15), drug/alcohol Intoxication (OR = 5.1; 95% CI 2.4-10.7), neurological Deficit (OR = 3.1; 95% CI 1.4-6.9), Seizure (OR = 3.7; 95% CI 1.8-7.8), and Skull fracture (odds ratio [OR] 24.5; 95% CI 16.0-37.3). Based on these results, the CIDSS2 risk score was created. The model C-statistic was 0.86 and performed similarly in children less than (C = 0.86) and greater than or equal to 2 years (C = 0.86). The CIDSS2 score is a novel tool to help physicians identify the minority of children with mTBI without ICI at increased risk for EIM, thereby potentially aiding hospital admission decisions. Copyright © 2018, Mary Ann Liebert, Inc.