IntroductionCrystal violet was commonly used for the treatment of oral and vaginal candidiasis or for sterilization during operations up to the 1960s. Because crystal violet is potentially toxic to mucosal membranes, it has been replaced with other disinfectants, and crystal violet is rarely used. We report a case of chemical cystitis due to intravesical instillation of crystal violet dye.Case presentationCrystal violet dye was instilled into the bladder of a 47-year-old Japanese woman to confirm the presence of a vesicovaginal fistula. Our patient developed symptoms of gross hematuria, frequent urination and lower abdominal pain. Computed tomography showed thickening of her whole bladder wall with spotted high-density lesions. Cystoscopy demonstrated desquamated epithelial cells and a hemorrhagic bladder wall. We treated our patient conservatively with nonsteroidal anti-inflammatory drugs and glucocorticoids. During follow-up, magnetic resonance images showed that the detrusor muscle of her bladder was normal. Our patient’s symptoms gradually improved and she completely recovered within six months.ConclusionConsidering the severe side effect of crystal violet, it would be better not to use this dye to examine conditions such as a vesicovaginal fistula. Magnetic resonance imaging may help to evaluate the level of damage in the bladder wall of patients with chemical cystitis.