Contrast media can be absorbed across the urothelium in amounts sufficient to cause severe anaphylactoid reactions. We report 2 cases of anaphylactoid reactions during voiding cystourethrography (VCUG) or retrograde pyelography (RGP). A retrospective review of 783 consecutive VCUGs or RGPs performed at our institution over the last five years revealed no other systemic contrast media reactions. Although our findings and a review of the literature discloses that the incidence appears to be extremely low, urologists and radiologists need to be aware that an anaphylactoid or vagal contrast medium reaction may develop during VCUGs or RGPs. In addition, these physicians need to be prepared to treat a reaction should one occur.