BACKGROUND: CT and MRI are both used for abdominal staging of pediatric renal tumors. The diagnostic performance of the two modalities for local and regional staging of renal tumors has not been systematically evaluated. OBJECTIVE: To compare the diagnostic performance of CT and MRI for local staging of pediatric renal tumors. MATERIALS AND METHODS: The study population was derived from the AREN03B2 study of the Children's Oncology Group. Baseline abdominal imaging performed with both CT and MRI within 30 days of nephrectomy was available for retrospective review in 82 renal tumor cases. Each case was evaluated for capsular penetration, lymph node metastasis, tumor thrombus, preoperative tumor rupture, and synchronous contralateral lesions. The surgical and pathological findings at central review were the reference standard. RESULTS: The sensitivity of CT and MRI for detecting capsular penetration was 68.6% and 62.9%, respectively (P = 0.73), while specificity was 86.5% and 83.8% (P = 1.0). The sensitivity of CT and MRI for detecting lymph node metastasis was 76.5% and 52.9% (P = 0.22), and specificity was 90.4% and 92.3% (P = 1.0). Synchronous contralateral lesions were identified by CT in 4/9 cases and by MRI in 7/9 cases. CONCLUSION: CT and MRI have similar diagnostic performance for detection of lymph node metastasis and capsular penetration. MR detected more contralateral synchronous lesions; however these were present in a very small number of cases. Either modality can be used for initial loco-regional staging of pediatric renal tumors.