Just as a pawnshop owner who is unable to distinguish a genuine Rolex™ watch from a cheap knockoff courts financial ruin, the physician who fails to discriminate between authentic myelodysplastic syndromes (MDS) and conditions resembling MDS risks misinforming or harming patients. This review summarizes minimal criteria for diagnosing MDS and discusses common diagnostic challenges. MDS needs to be separated from numerous neoplastic and non-clonal hematologic disorders that can mimic MDS, including other myeloid neoplasms, nutritional deficiencies, toxin exposures, aplastic anemia, and inherited disorders (e.g., congenital sideroblastic anemia). Some distinctions are more critical therapeutically than others; e.g., recognizing B12 deficiency is more important than parsing high-risk MDS from erythroleukemia. Diagnostically ambiguous cases may be assigned holding-pattern terms, "idiopathic cytopenia(s) of undetermined significance" (ICUS) or "idiopathic dysplasia of undetermined significance" (IDUS), while awaiting clarifying information or further clinical developments. In the future, advances in molecular pathology will improve diagnostic accuracy, especially in morphologically non-descript cases.