In the absence of genetic abnormalities, the diagnoses of myelodysplastic syndromes (MDS) is primarily based on the presence of dysplasia in blood and marrow cells. Currently, there is no standardized approach to evaluate dysplasia. International cooperative study groups like the European Working Group on MDS in Childhood (EWOG-MDS) depend, however, on a concordance in diagnoses by their national reference centres for morphology. In EWOG-MDS, the morphological diagnoses of all cases enrolled from Scandinavia, the Netherlands, Germany, the Czech Republic, Austria and Italy are established by five experienced pathologists or hematologists cooperating in a morphology board. To study their concordance in evaluating myelodysplastic disorders, members of the morphology board initiated blinded reviews of smears of blood and bone marrow aspirates of known cases. Four features of dysplasia in granulopoiesis, erythropoiesis and megakaryopoiesis were assessed on May-Grünwald-Giemsa stained smears. In a final review of six blinded cases, good concordance for these features was achieved among the five observers. Accurately defined and restrictively applied cellular features of dysplasia are an important tool to improve and ensure the concordance in the diagnosis of MDS among investigators. For cooperative groups, agreement on the evaluation of the morphological assessment of dysplasia is a prerequisite.