Abstract AIM: To compare the diagnostic accuracy of fluoroscopic voiding cystourethrography (VCUG) and voiding urosonography (VUS) under identical conditions. We performed VUS and VCUG simultaneously with the total time for both examinations taking no longer than the time required for either examination individually. MATERIALS AND METHODS: X-ray contrast medium and echo-contrast agent were mixed together in vitro , and echogenicity of the mixture was confirmed. A clinical study was then performed on 33 children who had a history of urinary tract infection. The bladder was filled using simultaneous administration of X-ray contrast medium and echo-contrast agent. VCUG and VUS were then performed simultaneously and evaluated separately by two specialists. RESULTS: Equivalent results were obtained for the two examinations in 61 of 66 renal tracts. Sensitivities of VUS and VCUG for the detection of VUR were 86% and 79%, respectively. The average time from catheterization to the completion of the study was 9.1 minutes – approximately as long as performing VCUG alone. CONCLUSIONS: First, the present simultaneous study is superior to previous comparisons, because the two examinations were performed under identical physiologic conditions. Second, our results suggest that the two techniques demonstrate similar sensitivity in the detection of reflux. Nakamura, M. et al. (2002). Clinical Radiology 57, 846–849.