Myelodysplastic syndrome (MDS) represents one of the most challenging health-related problems in the elderly, characterized by dysplastic morphology in the bone marrow in association with ineffective hematopoiesis. Hypoplastic MDS (h-MDS) accounts for 12-17% of all patients with MDS and has yet to be shown to alter the disease course or prognosis. The concept that T-cell-mediated autoimmunity contributes to bone marrow failure in MDS has been widely accepted due to hematologic improvement after immunosuppressive therapy. T-cell expansion is known to occur in these patients, but development of chronic T-cell disorders, especially T-prolymphocytic leukemia (PLL) in a hypocellular MDS is extremely rare, which has an aggressive course. The possible explanation for the association between the two disorders is that T-PLL might arise from a clonally arranged MDS stem cell. We report a unique case of h-MDS with non-progressive pancytopenia and severe hypocellular marrow for 2 years, followed by T-PLL within few months.