Intussusception occurs when a portion of the small or large intestine slides forward into itself, like a telescope. An intussusception can block flow through the intestines and also limit the blood supply to that area of intestine. It is most commonly seen in children who are younger than 1 year. The cause is usually unknown, but an intussusception can follow viral gastroenteritis (an infection) or intra-abdominal surgery or be caused by a tumor in the intestine. Although intussusceptions can occur anywhere in the small or large intestine, they are most commonly found near the transition from the small intestine to the large intestine. These types of intussusception are called ileocolic intussusceptions. The February 8, 2012, issue of JAMA includes an article about the risk of intussusception and rotavirus vaccines.