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.

CLL occurs more frequently in adults in their 60s. It is more common in men and is rarely seen in children.

Symptoms of CLL include weakness and fatigue, fever, night sweats, poor appetite, and weight loss. The spleen and lymph glands may become swollen and painful. Because the immune system doesn't work as well as it should, people with CLL may be more likely to get infections.