The appendix is also called the ileo-caecal appendix or the vermiform appendix. It is a small growth located in the caecum, from which it takes its name. The location of the appendix can vary from one individual to another. There are 3 main positions: sub-caecal, mid-caecal and retro-caecal. Anatomically, the appendix is a hollow diverticulum attached to the medial surface of the cecum, 3 cm below the ileal junction (at the junction between the small intestine and the colon). The appendix is vascularised by the appendicular artery, which arises from the ileo-caeco-colo-appendicular artery that follows the free edge of the meso.

The appendix is best known for its inflammation: appendicitis. Inflammation of the appendix usually requires its removal or appendectomy. The exact role of the appendix is not known. One can live without the appendix, but it contains immune cells that are useful in coordinating the intestinal response to attacks by pathogenic microorganisms. Some studies suggest that the appendix contains beneficial bacterial flora that are kept in reserve to respond to severe indigestion.