AIM To detect and verify the existence of a specific form of T-cell tumor accompanied by isolated lesions of bone marrow and aplastic syndromes. MATERIAL AND METHODS Four patients with aplastic syndromes were examined using clinical, histological, cytological, cytogenetic, and immunophenotypic methods. RESULTS Four cases of T-cell tumors of bone marrow with clinical and morphological manifestations of aplastic syndrome and scanty proliferation activity in bone marrow alone were diagnosed. The proliferation activity in bone marrow was observed as formation of small clusters composed of small-size lymphoid cells with dense nucleus. Dynamic monitoring of two patients revealed a trend toward an increase in the lymphoproliferation base against the remaining clinical picture of aplastic syndrome. The T-cell immunophenotype characterized by disappearance of some markers or decrease in their density, was observed only in some blood and bone marrow lymphocytes. The most significant changes of immunophenotype were observed in one of the patients (CD2+CD3-CD4-CD5-CD7-CD8-CD16-CD56-CD45RO++). The same patient had pronounced cytogenetic changes (47XY+Y, 47, XY, del(1)(p10) , 46 XY ) and resistance to routine therapy, including cyclosporin. In one patient the process transformed into lymphosarcoma. CONCLUSION The results obtained in four patients allow their clinicomorphological characteristics to be regarded as particular forms of T-cell tumors accompanied by bone marrow damage and aplastic syndrome.