What is it? A thin, hollow tube placed inside the ureter during surgery to ensure drainage of urine from the kidney into the bladder. J shaped curls are present at both ends to hold the tube in place and prevent migration, hence the description "Double J stent". Purpose? It allows the kidney(s) to drain urine by temporarily relieving any blockage, or to assist the kidney(s) in draining stone fragments freely into the bladder if definitive kidney stone surgery is carried out.