Chronic lymphocytic leukemia (CLL) is one of the chronic lymphoproliferative disorders (lymphoid neoplasms). It is characterized by a progressive accumulation of functionally incapable lymphocytes, which are usually of monoclonal origin. CLL disease with different manifestations is thought to be identical to mature (peripheral) B cell neoplasm with small lymphocytic lymphoma (SLL), one of the indolent non-Hodgkin’s lymphomas. The term CLL is used when the disease is primarily manifested in the blood, while the term SLL is used when the involvement is primarily nodular. The assessment of suspicious cases varies depending on the presentation. The diagnosis of CLL is usually suspected in an adult who is found to have absolute lymphocytosis. Assessment of such patients should include a complete laboratory treatment in which the basis is a blood picture with differential distribution, peripheral blood flow cytometry to determine the immunophenotype of circulating lymphocytes; and examination of the peripheral smear. Bone marrow evaluation is not usually required, but is included in the assessment of patients with unexplained cytopenias. The nurse plays an important role in caring for patients with CLL, preparing patients for diagnostic and blood sampling.