One-hundred and eighty-eight patients with chronic lymphocytic leukemia were analyzed for prognosis based on Rai's staging system. It was found that stages I and II were not homogeneous as to prognosis. Stage II patients presenting with isolated splenomegaly had a long survival and were pooled with stage 0 patients (low risk group, 30% of cases, relative death rate 0.24, median survival greater than 10 yr). Stages I and II patients with a lymphocyte count higher than 40 x 10(9)/liter had a short survival and were pooled with stages III and IV patients (high risk group, 39% of cases, relative death rate 1.91, median survival 3.3 yr). Stages I and II patients with a lymphocyte count lower than 40 x 10(9)/liter made up an intermediate or standard risk group (31% of cases, relative death rate 1.00, median survival 6.2 yr). This modified staging system applied successfully to both old and young patients (more and less than 60 yr old, respectively).