A 45-year-old white man was hospitalized with gross hematuria, 1 month after cystoscopy and biopsy for the same complaint. The biopsy revealed cystitis glandularis. One day after admission, he developed seizures and died within hours. Autopsy, laboratory tests, and further questioning of hospital staff showed that he died of acute hyponatremia and massive intravascular hemolysis after irrigating the bladder with sterile water. Until his case, this fatal complication had been described only during transurethral surgery. Accidental injury and death due to diagnostic and therapeutic procedures in hospitals have been reviewed and reported by other authors, and deaths often occur during anesthesia and surgery. Sudden death due to natural causes is also common in the hospital, and differentiating between natural and accidental iatrogenic death can be difficult. The reported case demonstrates that even the most seemingly innocuous medical procedures can prove fatal and that a thorough medicoelgal investigation is essential in cases of unexpected hospital deaths. 8 references and 4 figures