The name of Giovanni Di Guglielmo is inscribed in the history of haematology as a result of his recognition that cells of the erythroid and megakaryocytic lineages could be involved in a process that was analogous to the involvement of the granulocytic lineage in leukaemia. Furthermore, he recognized bilineage and trilineage involvement in these processes, foreshadowing the later descriptions of various myeloproliferative disorders. Di Guglielmo gave his name to Di Guglielmo's disease (acute erythraemia, acute erythraemic myelosis or pure erythroid leukaemia) and Di Guglielmo's syndrome (encompassing pure erythroid neoplasms and their transition to a mixed erythroid-granulocytic lineage proliferation and pure myeloblastic proliferation). Although these terms are now little used, the concepts first formulated by Di Guglielmo in 1917 were prescient and now, more than 80 years later, their validity is undoubted.