Intravesicular formaldehyde has been used for intractable hemorrhagic cystitis since the late 1960's. Initial reports described few complications, but in the 1970's both ureteral as well renal parenchymal damage were reported in the urology literature. This has been less appreciated by nephrologists perhaps related to the paucity of reports in the nephrology literature. Although the pathogenesis has not been rigorously studied ureteral toxicity may be secondary to intense edema, inflammation and subsequent fibrosis induced by the formaldehyde; while renal tubular injury may be secondary to systemic absorption of formaldehyde. Ureteral reflux as well as dosage of intravesicular formaldehyde seem to be risk factors for acute renal failure. We describe a case of acute renal failure secondary to intravesicular formaldehyde and review pathogenesis as well as potential prophylactic measures to prevent this complication.