The authors describe a 15-year-old boy with hepatosplenic gammadelta T-cell lymphoma associated with hemophagocytic syndrome (HPS) along with isochromosome 7q and trisomy 8. He presented with prolonged fever, mild anemia, thrombocytopenia, and hepatosplenomegaly. Physical examination, radiography, and ultrasound tomography revealed no lymphoadenopathy. He had elevated levels of serum ferritin, interferon-gamma, soluble interleukin-2 receptor, and interleukin-6. Bone marrow aspirate showed hypercellularity with 50% lymphoblasts and erythrophagocytosis of macrophage. A cytogenetic study of bone marrow revealed an abnormal karyotype, 47,XY,I(7q),+8, in 5/30 cells. Clonal rearrangement of the genes for T-cell receptor gamma and delta chains was elucidated by polymerase chain reaction. He achieved a complete remission after intensive chemotherapy and underwent splenectomy 18 months after diagnosis. Although the patient was clinically in remission, minimal residual disease (MRD) was detected in the removed spleen by polymerase chain reaction. This might mean that this type of lymphoma is refractory, as reported previously, and might indicate that marrow ablative therapy is needed to achieve a cure. The present case illustrates the usefulness of MRD analysis, and MRD studies in this group of disorders may be helpful in the decision of whether to continue a more aggressive therapeutic approach.