The triad of thiamine-responsive anaemia, diabetes mellitus and deafness has been reported in 15 patients with macrocytic anaemia, sometimes associated with moderate thrombocytopenia. The bone marrow aspirate usually shows megaloblastic changes and ringed sideroblasts. However, tri-lineage myelodysplasia has never been reported. We describe two patients who presented with diabetes, deafness and thiamine-responsive pancytopenia. Bone marrow aspirate and biopsy were typical of tri-lineage myelodysplasia. These findings suggest that thiamine may have a role in the regulation of haemopoiesis at the stem cell level. We propose the term 'thiamine-responsive myelodysplasia' rather than that of thiamine-responsive anaemia.