BACKGROUND: Pre-operative assessment of intravascular extension of Wilms tumor is essential to guide management. Our aim is to evaluate the diagnostic performance of multidetector CT in detection of tumor thrombus in Wilms tumor. PROCEDURE: The study population was drawn from the first 1,015 cases in the AREN03B2 study of the Children's Oncology Group. CT scans of children with (n = 62) and without (n = 111) tumor thrombus at nephrectomy were independently reviewed by two radiologists, blinded to patient information. Doppler sonography results were obtained from institutional radiology reports, as Doppler requires real-time evaluation. The diagnostic performance of CT and Doppler for detection of tumor thrombus was determined using nephrectomy findings as reference standard. RESULTS: In the primary nephrectomy group, tumor thrombus detection sensitivity, specificity of CT was 65.6, 84.8%, and Doppler was 45.8, 95.7%, respectively. In this group, sensitivity of CT, Doppler for detection of cavoatrial thrombus was 84.6 and 70.0%, respectively. In the secondary nephrectomy group, tumor thrombus detection sensitivity, specificity of CT was 86.7, 90.6%, and Doppler was 66.7, 100.0%, respectively. In this group, sensitivity of CT, Doppler for detection of cavoatrial thrombus was 96.0 and 68.8%, respectively. Pre-operative Doppler evaluation performed in 108/173 cases, detected 3 cases with intravenous extension (2 in renal vein, 1 in IVC at renal vein level) that were missed at CT. CONCLUSIONS: CT can accurately identify cavoatrial tumor thrombus that will impact surgical approach. Routine Doppler evaluation, after CT has already been performed, is not required in Wilms tumor. Pediatr Blood Cancer 2012; 58: 551-555. (c) 2011 Wiley Periodicals, Inc.