We describe a 70-year-old man with fulminant adult T-cell leukemia/lymphoma. He died of progressive disease 1 week after the onset of symptoms. The integrated viral DNA of human T-lymphotropic virus type I was detected in the bone marrow aspirate by polymerase chain reaction. Cytogenetic analysis of bone marrow cells showed novel clonal aberrations consisting of 46,XY,der(8)t(8;14)(p11;q11),del(9) (q13q22),t(14;22)(q13;q13).