Monarch Disease Ontology identifier MONDO_0003864 (chronic lymphocytic leukemia/small lymphocytic lymphoma) is an indolent, mature B-cell neoplasm composed of small, round B-lymphocytes. When the bone marrow and peripheral blood are involved, the term chronic lymphocytic leukemia is used. The term small lymphocytic lymphoma is restricted to cases which do not show leukemic involvement of the bone marrow and peripheral blood. Also known as: CLL/SLL, chronic lymphocytic leukemia/small lymphocytic lymphoma (morphologic abnormality).