OBJECTIVE Ureterocele eversion refers to the sudden appearance of a bladder diverticulum at the site of ureterocele compression during voiding cystourethrography (VCUG). The radiologic appearance closely resembles a congenital bladder (paraureteral) diverticulum. Distinguishing ureterocele eversion with vesicoureteral reflux in duplex kidneys from congenital bladder diverticula with reflux is important for preoperative planning. This study describes the findings of ureterocele eversion and lower pole vesicoureteral reflux in duplex kidneys on VCUG and demonstrates how its appearance can be misleading. METHODS Medical records, sonograms, and cystograms were reviewed retrospectively for 12 children who had VCUGs demonstrating bladder diverticula with vesicoureteral reflux and who, at surgery, had ureteroceles associated with duplex systems. Each case was assessed as to whether the finding of a diverticulum with reflux on VCUG had been correctly interpreted as ureterocele eversion with lower pole vesicoureteral reflux. RESULTS Diagnosis of ureterocele eversion with lower pole reflux was uncertain or misinterpreted as congenital bladder diverticula with reflux in five patients in whom ureteroceles were not identifiable or in whom reflux occurred into what resembled single systems rather than lower poles of duplex systems. In two patients in whom ureteroceles were not initially identified, fluoroscopy recognized ureterocele eversion with lower pole reflux. Sonography confirmed ureterocele in one of these patients, and cystoscopy in the other. CONCLUSIONS Ureterocele eversion with lower pole vesicoureteral reflux is readily diagnosed by VCUG when a ureterocele is initially identified or if the fluoroscopic appearance is typical. Ureterocele eversion with lower pole reflux can be mistaken for a congenital paraureteral diverticulum with reflux into a single collecting system if the ureterocele is small or not initially detected or if the refluxed system is not recognized as a lower pole moiety.