Background Computed tomography is commonly used to rule out intra-abdominal injury (IAI) in children, despite associated cost and radiation exposure. Our purpose was to derive a prediction rule to identify children at very low risk for IAI after blunt abdominal trauma (BAT) for whom a CT scan of the abdomen would be unnecessary. Study Design We prospectively enrolled children younger than 16 years of age who presented after BAT at 14 Level I pediatric trauma centers during 1 year. We excluded patients who presented more than 6 hours after injury or underwent abdominal CT before transfer. We used binary recursive partitioning to derive a prediction rule identifying children at very low risk of IAI and IAI requiring acute intervention (IAI-I) using clinical information available in the trauma bay. Results We included 2,188 children with a median age of 8 years. There were 261 patients with IAI (11.9%) and 62 patients with IAI-I (2.8%). The prediction rule consisted of (in descending order of significance): aspartate aminotransferase >200 U/L, abnormal abdominal examination, abnormal chest x-ray, report of abdominal pain, and abnormal pancreatic enzymes. The rule had a negative predictive value of 99.4% for IAI and 100.0% for IAI-I in patients with none of the prediction rule variables present. The very-low-risk population consisted of 34% of the patients and 23% received a CT scan. Computed tomography frequency ranged from 4% to 96% by center. Conclusions A prediction rule using history and physical examination, chest x-ray, and laboratory evaluation at the time of presentation after BAT identifies children at very low risk for IAI for whom CT can be avoided.