An 82-year-old female developed hemolytic uremic syndrome (HUS) after a prodromal illness of bloody diarrhea. No specific enteric pathogen was isolated. A renal biopsy performed 5 days after the onset of azotemia revealed typical thrombotic microangiopathy. By electron microscopy, massive annular-tubular deposits admixed with fibrillar fibrin were demonstrated in glomerular capillaries. Immunofluorescent staining of the intracapillary material was positive for IgG, IgM, C<sub>3</sub>, C<sub>1</sub>q and fibrin-related antigens. No evidence of plasma cell dyscrasia, cryoglobulinemia or systemic lupus erythematosus was found, and the patient recovered renal function uneventfully in 2 months. Organized immune deposits appear to have played a role in the pathogenesis of HUS in this patient.