Chronic lymphocytic leukemia (CLL) is a type of cancer that causes the body to produce large numbers of white blood cells (lymphocytes). These lymphocytes, called leukemia cells, cannot fight infection very well.

When leukemia cells build up in the blood and bone marrow, there is less room for healthy blood cells. This can cause infections, anemia, and easy bleeding.

CLL usually gets worse slowly. It is sometimes referred to as chronic lymphoblastic leukemia.