Retrograde pyelography is used to evaluate upper collecting system in patients with hematuria who have contrast allergy. Reported here is a patient who developed severe, late-onset anaphylactoid reaction after retrograde pyelography. Premedication is commonly used to reduce risk of allergic reaction but has limited evidence to support its efficacy. Caution should be used when evaluating microhematuria with retrograde pyelography in patients with prior anaphylactoid reaction to intravenous contrast.