Indigo carmine (sodium indigotin disulfonate) is a blue dye that is generally regarded as a safe and inactive material. It is widely used in urology and gynecology to identify the ureteral orifice. Occasionally it causes high blood pressure, bradycardia, nausea and vomiting as side effects. Though rare, it can cause a skin rash, pruritus, and bronchospasm as well. However, it is known that hypotension is extremely uncommon. We report an experience of extreme hypotension that happened immediately after an intravenous indigo carmine injection during a radical prostatectomy under general anesthesia.