Thiamine-responsive megaloblastic anemia syndrome (TRMA) is an autosomal recessive disorder with features that include megaloblastic anemia, mild thrombocytopenia and leukopenia, sensorineural deafness and diabetes mellitus. In this disease, the active thiamine uptake into cells is disturbed. Treatment with pharmacological doses of thiamine ameliorates the megaloblastic anemia and diabetes mellitus. Previous studies have demonstrated that the disease is caused by mutations in the SLC19A2 gene encoding a high-affinity thiamine transporter. We present a 5-yr-old-boy with TRMA and, because of its rarity, we review the literature.