We report a rare case of T-cell acute lymphoblastic leukemia (T-ALL) with an aberrant phenotype. A 52-year-old man was admitted to our hospital because of lymph node (LN) swelling in the bilateral neck. A computed tomographic scan showed LN swelling in the mediastinum and a right pleural effusion. The tumor cells in the neck LN showed positivity for cytoplasmic CD3, CD7, CD19, and CD79a, whereas the tumor cells in the bone marrow (BM) showed positivity for CD10 and CD13 in addition to the former 4 antigens. The chromosomes in the BM were normal. Neither T-cell receptor gamma nor immunoglobulin heavy chain rearrangement was detected in the neck LN. We diagnosed this case as T-ALL with an aberrant phenotype and started the standard chemotherapy for ALL. The response was so effective that complete remission (CR) was easily attained. The patient is now under maintenance therapy in the first CR without hematopoietic cell transplantation.