The first of case of adult T-cell prolymphocytic lymphosarcoma is reported which according to the natural course, cell composition of tumor, cell surface markers as well as expressed immune response to a wide spectrum of HTLV-1 gag an env encoded proteins can be classified as HTLV-associated adult T-cell leukemia. Diagnosis of the tumor alongside with identification of HTLV-1-infected individuals in the USSR emphasizes the need to stimulate research in HTLV-1-associated carcinogenesis in this country.