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The diagnosis of myelodysplastic syndromes (MDS) is based on morphology and cytogenetics. However, limited information is currently available on the interobserver concordance of the assessment of dysplastic lineages (10% or ≥10% in bone marrow (BM)). The revised International Prognostic Scoring System (IPSS-R) described a new threshold (2%) for BM blasts. However, the interobserver concordance of the categories (0-≤2% and2-5%) has limited data. The purpose of the present study was to investigate the assessment of dysplastic lineages and IPSS-R reproducibility. Our study was divided into two Steps. In each Step, the microscopic examinations were performed separately by two morphologists. Regarding the category of BM blasts ≤2% and2-5%, interobserver agreement was more than 'moderate' in all pairs (kappa test: 0.43-0.90). Regarding dysgranulopoiesis (dysG) and dyserythropoiesis (dysE) in BM, interobserver agreement was more than 'moderate' in all pairs (kappa test, dysG: 0.45-0.96, dysE: 0.45-0.81). Regarding the category of dysmegakaryopoiesis (dysMgk) in BM, interobserver agreement was more than moderate in 4 out of 5 pairs (kappa test: 0.58-1.00), and was fair for one pair (kappa test: 0.37). We consider that high interobserver concordance may be possible for the BM blast cell count (≤2% or2-5%) and dysplasia (10% or ≥10%) of each lineage.