Background. The significance of flow cytometry indicating myelodysplasia without proof of myelodysplasia by cytomorphology remains to be clarified. Design and Methods. In 142 patients analyzed in parallel by flow cytometry, cytomorphology and cytogenetics for suspected myelodysplasia without proof of myelodysplasia by cytomorphology we evaluated follow-up analyses. Results. At initial assessment flow cytometry indicated myelodysplasia in 64/142 (45.1%) patients. In 9/142 (6.3%) patients cytogenetics revealed aberrant karyotypes at first evaluation which was true for 5/64 (7.8%) patients rated myelodysplasia by flow cytometry. The remaining 133 patients without proof of myelodysplasia by cytomorphology and with normal karyotype were subject to follow-up analyses that confirmed myelodysplasia by cytomorphology, cytogenetics or molecular-genetics in 47 (35.3%) after a median interval of 9 months (range 1-53). Regarding initial flow cytometry results this applied to 30/59 (50.1%) with myelodysplasia, 10/42 (23.8%) with possible myelodysplasia (minor antigen aberrancies only) and 7/32 (21.9%) without myelodysplasia (p=0.004). Notably, in the latter 7 patients flow cytometry results changed at follow-up to possible myelodysplasia (n=4) and myelodysplasia (n=2). Conclusions. This data argues in favour of including flow cytometry besides cytomorphology, cytogenetics and molecular-genetics to diagnose myelodysplasia and suggests a closer monitoring of patients with myelodysplasia-typical aberrant antigen expression found by flow cytometry.