A Japanese male patient with myelodysplastic syndrome (MDS) was shown to have associated Tn syndrome; the first report of Tn syndrome with MDS. The Tn expression was demonstrated on erythrocytes, granulocytes, monocytes, platelets, and lymphocytes by flow cytometric analysis using a lectin and an antibody. Electrophoresis of erythrocyte membrane proteins revealed slower mobility of glycophorin B from the patient than that from normal individuals, suggesting a glycophorin B molecular abnormality.