In a retrospective study it was endeavoured to evaluate the effects of splenectomy in chronic lymphocytic leukaemia (CLL) characterised by splenomegaly. The material comprises 42 patients subjected to the operation in the course of the past 20 years. In the majority the spleen weighed more than 1000 g. The main indication for splenectomy was anaemia, while in 9 cases it was thrombocytopenia and in 14 cases hypercatabolism. Splenectomy is followed by a pronounced increase in the venous haemoglobin level and platelet count to higher values which have been recorded for up to 3 years after the procedure. In cases where data were available, there has been weight gain and a falling basal metabolic rate. Splenectomy is effective especially in cases predominated exclusively by splenomegaly, but even in cases with marked extrasplenic manifestations, splenectomy often greatly reduces the need for prednisone and cytostatics. Increasing hepatomegaly and lymphomas were not more common after splenectomy than in a control series, and the incidence of infections was not increased after the operation. For comparison, 37 non-splenectomised patients with splenomegaly were assessed. X-radiation of the spleen seems to be insufficient, since usually it has to be repeated. Splenomegaly does not decrease spontaneously and rarely after treatment with prednisone/cytostatics. The findings indicate that splenectomy of patients with CLL and increasing splenomegaly should be performed more often and presumably also earlier than recommended in the literature.