Your spleen is an organ above your stomach and under your ribs on your left side. It is about as big as your fist. The spleen is part of your lymphatic system, which fights infection and keeps your body fluids in balance. It contains white blood cells that fight germs. Your spleen also helps control the amount of blood in your body, and destroys old and damaged cells.
Certain diseases might cause your spleen to swell. You can also damage or rupture your spleen in an injury, especially if it is already swollen. If your spleen is too damaged, you might need surgery to remove it. You can live without a spleen. Other organs, such as your liver, will take over some of the spleen's work. Without a spleen, however, your body will lose some of its ability to fight infections.