We present a case of large cell lymphoma in a 20-year-old Oriental male who presented with massive splenomegaly and mild anemia. Surface marker and molecular genetic analyses of lymphomatous cells obtained from the spleen indicated a T-cell origin. Chromosomal analysis identified an isochromosome 7q as the sole abnormality. This is the first report of isochromosome 7q as the sole cytogenetic abnormality in a T-lineage malignant clonal expansion.