Trisomy 4 has been identified previously as a chromosome abnormality associated with acute nonlymphocytic leukemia (ANLL) with myelomonocytic lineage and in myelodysplastic syndromes (MDS). We report a case of acute lymphocytic leukemia (ALL) (French-American-British, FAB L1) in a 42-year-old Japanese man, with trisomy 4 as the sole chromosomal anomaly. Immunophenotypically, the leukemic blasts demonstrated reactivity with CD2, CD5, and CD7 and indicated on early stage of T cell.