An indolent (slow-growing) type of lymphoma in which too many immature lymphocytes (white blood cells) are found mostly in the lymph nodes. This causes the lymph nodes to become larger than normal. Sometimes cancer cells are found in the blood and bone marrow, and the disease is called chronic lymphocytic leukemia. The disease is most often seen in people older than 50 years. SLL is a type of non-Hodgkin Lymphoma. Also called small lymphocytic lymphoma and well-differentiated lymphocytic lymphoma.