Chemical cystitis due to intravesical instillation of gentian violet or crystal violet is rare and all of the reported cases have been in adults using undiluted solution, which resulted in long-term sequelae. This is a case report on a 16-month-old boy with hemorrhagic cystitis after the instillation of diluted gentian violet into the bladder to rule out bladder injury during inguinal herniorrhaphy. Although he was completely recovered with conservative therapy, gentian violet, even when diluted, should not be used on the urinary tract.