Adverse reactions associated with the parenteral use of contrast agents are widely recognized, but reactions to contrast agents used in micturating cystourethrography (MCU) are much less common, although absorption of contrast media through intact bladder mucosa has been documented. A significant adverse reaction to ionic contrast material used for MCU in which neither reflux nor traumatic urethral catheterization could be implicated is presented. This case illustrates that significant reactions can occur during MCU and appropriate resuscitation facilities must be available. In a patient with a history of reaction to IV contrast media, the need for MCU should be reviewed and consideration given to nuclear medicine MCU. If a radiologic MCU is needed, consideration should be given to performing it in the hospital, with nonionic contrast media and steroid premedication.