Myelodysplastic syndromes (MDS) comprise a heterogenous group of clonal disorders of hematopoietic progenitors, showing genetic instability and in many cases progression to acute myeloid leukemia (AML). When MDS progress towards AML (AML/MDS), additional genetic lesions cause a block in differentiation and an accumulation of blast cells. Hence, both pathophysiologically and clinically the MDS and AML/MDS phases are distinguishable. Leukemia cell lines are key resources for modelling hematological malignancies. Characterization of these cell lines has provided a rich vein of insights into the mechanisms underlying malignant transformation. Some 31 cell lines have been described in the literature purportedly established from patients with MDS. However, a significant minority of these has proved false after DNA profiling which revealed their cross-contamination with older established leukemia cell lines. Most remaining ("authentic") MDS cell lines were established during the leukemic phase of the disease progression rather than during the MDS phase. Based on these data we have assigned the 31 candidate MDS cell lines to one of the three categories: (1) false (cross-contaminated) cell lines and non-malignant cell lines; (2) malignant cell lines established in the AML/MDS leukemic phase; and (3) apparently legitimate MDS cell lines established during the MDS phase. While MDS and AML/MDS cell lines both provide singular resources for modelling pathology, mining oncogenically modified macromolecules, and testing druggability, we contend these groups should be considered separately.