A 67-year-old woman who had underlying rheumatoid arthritis and diabetes mellitus had an 8-year history of recurrent hemorrhagic cystitis. During her most recent episode of cystitis, a specimen of urine yielded herpes simplex virus type 2 in culture. A biopsy of the bladder mucosa revealed intranuclear inclusions in multinucleated and mononuclear giant cells that were positive for herpes simplex virus type 2 by immunoperoxidase staining. She had no evidence of infection with herpes simplex virus outside her bladder.