Chronic lymphocytic leukemia (CLL) is the most common type of leukemia in the western hemisphere. Diagnosis and staging of CLL are usually straightforward, but predicting an individual patient's prognosis is still a challenge. Cytogenetic abnormalities provide important prognostic information in CLL and may show its molecular heterogeneity. A search for oncogene abnormalities continues, although no consistent defects have been identified. New agents such as fludarabine produce high complete remission rates and have generated interest in earlier treatment as a first step in a potential cure. Fludarabine also makes autologous bone marrow transplant feasible as a consolidation therapy. Immunologic abnormalities and minimal residual disease persist in most patients in remission. Combining fludarabine with other active agents and devising effective postremission strategies may change the natural history of CLL.