In this report the clinical, morphologic, histologic and immunologic findings of 41 patients with hairy lymphoid cells in peripheral blood and/or bone marrow are analyzed. In 27 patients the diagnosis of hairy cell leukemia was established. 14 patients had other variants of lymphoproliferative disorders: malignant lymphoma with hairy cells--7, chronic lymphocytic leukemia with hairy cells--5, and T cell lymphoproliferative disorder with hairy cells--2 patients, respectively. Several variants of malignant lymphoma with hairy cells were defined: lymphocytic, centrocytic and lymphoplasmacytic. The importance of combined use of bone marrow biopsy and immunophenotyping for the correct diagnosis of hairy cell leukemia and other "hairy-cell" lymphoproliferative disorders is stressed. The obtained data suggest relationship between characteristic clinical manifestation (isolated splenomegaly), presence of hairy cells and CD11c-antigen expression.