Myeloproliferative neoplasms (MPN) have been characterized by their clinical and histological patterns and have also been accordingly subclassified. Several specific genomic abnormalities are identifiable, raising the possibility of introducing a new era of genotype classification for an updated MPN classification. MPN classified by clinical and hematological data have specific histopathological characteristics of JAK2, MPL, and CALR abnormalities. Herein, the author will endeavor to devise an algorithm for MPN diagnosis based on bone marrow histology. Cellularity, erythroid islet formation, size, nuclear morphology, and the distribution pattern of megakaryocytes are the specific findings indicative of differences in genotype abnormalities.