A splenectomy is surgery to remove the entire spleen, a delicate, fist-sized organ that sits under the left rib cage near the stomach. The spleen is an important part of the body's defense (immune) system. It contains special white blood cells that destroy bacteria and help the body fight infections when you are sick. It also helps remove, or filter, old red blood cells from the body's circulation.

If only part of the spleen is removed, the procedure is called a partial splenectomy.

Unlike some other organs, like the liver, the spleen does not grow back (regenerate) after it is removed.

Up to 30% of people have a second spleen (called an accessory spleen). These are usually very small, but may grow and function when the main spleen is removed. Rarely, a piece of the spleen may break off with trauma, such as after a car accident. If the spleen is removed, this piece can grow and function.