20 patients with hairy cell leukemia were treated between 1966 and 1978. All modalities of treatment for lymphoproliferative disorders have been used in at least some patients. Besides prednisone, vincristine, cyclophosphamide and their combinations as well as irradiation of enlarged spleens, cell depletion was achieved by splenectomy and leukapheresis. Cytostatics had no beneficial effect. Cytostatic therapy exposed some patients to the hazards of severe infections. On the contrary splenectomy lead to the improvement of some blood parameters. Leukapheresis seemed to work nearly identically. The survival of the splenectomized patients was longer than of controls. Because of the variability of the duration of the disease no definite statement could be made concerning the survival of both groups. 12 patients died during the observation period. Splenectomy was followed by one death, 11 patients died of septicemia.