When analyzing 20 cases of hairy-cell leukosis we can compare a group with a medium survival time (16 months since clinical beginning of the illness) to a group with a long survival time (80 months). Patients (historically older) with short survival times are characterized by a combination of short anamnestic dormancy, younger age, severe symptoms and the applying of a steroid and cytostatic therapy instead of splenectomy. Prevalent causes of death were infections which seemed to increase by cytostasis. Patients with a longer survival time were characterized by a longer survival time were characterized by a longer anamnestic dormancy (up to 15 years), and clinically bland indications that permitted splenectomy. In this group we find interesting cases in which after splenectomy the infiltration of the bone marrow was greatly reduced, being in one case merely 10% after 10 years. These findings ought to be discussed with respect to the aspect of the extremely slow and spleen dependent kinetics of the pathognomy of the cell fractions. As to the origin of the hairy cells and to mark the difference to other lymphomas of the spleen it is necessary to stress the fact that the rate of immunoglobuline did not change in any of the 20 cases observed.