Background: Patients with Crohn's disease (CD) are frequently subjected to computed tomography (CT) in the emergency department (ED). This young population is at higher risk of malignancy from radiation exposure. Objectives: We aimed to validate a decision tool predicting complications (perforation, abscess or other serious finding) on imaging at two sites. Methods: We conducted a retrospective review of CT outcomes among patients with CD with ED visits at two tertiary care centers. Inclusion criteria were a CT of the abdomen/pelvis with contrast and complete lab data (erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP)) within 24 hours of arrival at the University of Michigan (UM) (2012-2013) and the University of Pittsburgh (UPMC) (2009-2012). Sensitivity, negative predictive value (NPV), miss rate and CT avoidance rate were calculated. Results: At UPMC (n=210), the tool had a sensitivity of 88.9% and NPV of 98.0%, potentially saving 47.1% from CT with a miss rate of 1.0%. At UM (n=248), the tool had a sensitivity of 90.9% and NPV of 96.0%, saving 40.3% from CT with a miss rate of 1.6%. Conclusion: A decision tool using CRP and ESR predicting CT outcomes among CD patients performed well in an external validation, allowing providers to forgo CT use with a low miss rate.