Analysis of the disease course in 17 patients afflicted with hairy-cell leukemia enabled the authors to specify 3 clinico-hematologic variants of the disease: a typical or a splenic one (with a predominant injury to the spleen), an atypical or bone marrow one (with a predominant injury to bone marrow), and a hypoplastic one. The bone marrow variant was characterized by the most pronounced leukemic injuries to bone marrow, severe bacterial complications, and the most unfavourable prognosis. The remaining variants were marked by their own individual features and ran a more favourable course. The division of hairy-cell leukemia into 3 variants promotes the improvement of the disease diagnosis and the elaboration of the optimal treatment policy in each specific case as well as the disease prognosis. The pathogenetic heterogeneity of the hairy-cell leukemia variants is discussed.