We describe the clinical and laboratory features of an unusual case with Sezary cell-like leukemia. Clinical manifestations were: anemia (Hb 9.4 g/dl), severe thrombocytopenia (5 x 10(9)/l), lymphocytosis (43 x 10(9)/l) and splenomegaly. There was no lymphadenopathy, hepatomegaly or skin lesions. Bone marrow trephine showed diffuse infiltration by atypical lymphoid cells. By ultrastructural analysis the cells were small to medium-size lymphocytes with nuclear features identical to Sezary cells. Immunophenotyping showed that most peripheral blood mononuclear cells were negative with B lymphoid, myeloid, and stem cell-associated markers and were also negative with most T lymphoid markers (CD2, CD4, membrane/cytoplasmic CD3, CD5 and CD8). However, they were positive with CD38 (70%), CD7 (25%) and TIA-2 (25%). Molecular analysis showed a clonal rearrangement of the TCR beta and gamma chain genes. The patient was initially treated with vincristine, doxorubicin and asparaginase and then with six cycles of CHOP, achieving a complete remission and remaining free of disease 22 months from diagnosis. Aberrant immunophenotypes are not frequent in primary T cell leukemias. This is the first case of a rare type of T cell neoplasm, Sezary cell-like leukemia, in which cells lacked most of the T cell-associated antigens.