BACKGROUND: The presentation of appendicitis in pediatrics is variable, and diagnostic imaging is often used. Magnetic resonance imaging (MRI) is replacing computed tomography in some centers, particularly after a nondiagnostic ultrasound (NDUS). Nonetheless, MRI is not widely used in this setting because of cost, procedure time, institutional capacity, and high rates of negative scans. We hypothesized that the Alvarado Score (AS) could be used to determine the additive diagnostic value of MRI after an NDUS. MATERIALS AND METHODS: Retrospective review of patients aged ≤18 y at a single tertiary care children's hospital who received an ultrasound for suspected appendicitis during 10 consecutive months in 2017. NDUS were defined as nonvisualization of the appendix or secondary signs without radiologic diagnosis. AS were retrospectively calculated from the electronic medical record. Primary outcomes were pathology-confirmed appendicitis, appendectomy, and perforation. RESULTS: AS was determined for 352 patients out of 463 who met inclusion criteria (76%). Sixty-two percent had an NDUS, and 45% of these patients received MRI. Patients with high-risk AS were significantly more likely to have MRI diagnostic of appendicitis (P = 0.0015), and low-risk AS patients were more likely to have a negative or equivocal MRI (P = 0.0169). Twenty-one MRI scans were required per each additional diagnosis of appendicitis in patients with low AS after NDUS versus 4.2 in intermediate-risk AS patients and 2.1 in high-risk AS patients. CONCLUSIONS: Risk stratification with AS can help assess the additive diagnostic utility of MRI after NDUS. MRI may be overutilized for diagnosing acute appendicitis in pediatric patients with low-risk AS.