Lymph nodes were examined from 41 cases of typical chronic lymphocytic leukemia (CLL). Degree of immaturity was graded as absent to minimal (Grade I), moderate (Grade II) and marked (Grade III). A moderate degree of immaturity was found in the lymph node in 14 of 41 cases even though the cells seen on the initial bone marrow and peripheral blood smears obtained from these patients were essentially all mature. The morphology of these nodes could be confused with poorly differentiated lymphocytic or mixed lymphocytic-histiocytic lymphoma in terms of the degree of immaturity present. A marked degree of immaturity present. A marked degree of immaturity was found in 5 cases; the morphology of these cases resembled histiocytic lymphoma. In the remaining 22 cases immaturity was essentially absent. The morphology of these cases was similar to that of diffuse well differentiated lymphocytic lymphoma. Our studies suggest that a moderate degree of immaturity in the lymph node of patients with CLL does not indicate that these patients will have a marked shortening of their survival.