Peripheral T-cell proliferative disease is a group of systemic diseases that exhibit considerable heterogeneity in clinical findings, morphologic pattern, immunology, and prognosis. The morphology of neoplastic T-cells varies from mature small lymphocytes to malignant lymphoid cells. Latent Epstein-Barr virus (EBV) infection of the peripheral T-cells is found in majority of cases. Inflammatory cytokines (such as tumor necrosis factor-α), which are secreted from EBV-infected T cell and/or activated macrophages, are related to hemophagocytosis, severity of disease and outcome of patients.