['To evaluate the sensitivity and specificity of CD34 staining of megakaryocytes (MKs), in order to distinguish non-neoplastic and neoplastic bone marrows (BMs).', 'Three hundred BMs (120 non-neoplastic and 180 neoplastic) were evaluated for percentage and intensity of CD34 staining of MKs. The selected non-neoplastic cases included anaemia, autoimmune conditions, immune thrombocytopenia (ITP), and staging BMs. The neoplastic cases included myelodysplastic syndromes and/or myeloproliferative neoplasms (MDS, MPN, MDS/MPN). Eight per cent of non-neoplastic (9/120) cases and 13% of neoplastic (24/180) cases showed ≥30% CD34+ MKs, and these were essentially restricted to cases of megaloblastic anaemia (MBA) and non-acute myeloid neoplasms. The finding of ≥30% CD34+ MKs did not distinguish between categories of non-acute myeloid neoplasms. MDS cases with ≥30% CD34+ MKs had lower platelet counts than cases with <30% (P = 0.03).'] Do cD34+ megakaryocytes ( ≥30 % ) are associated with megaloblastic anaemia and non-acute myeloid neoplasia?