The present case report of SM-ET is the first one diagnosed according to the recent revision of WHO diagnostic criteria for both ET and SM [5], as the four major criteria for ET (platelet count ≥ 450 × 109/L, typical bone marrow histology, presence of JAK2 V617F mutation and absence of criteria for other myeloproliferative neoplasms) were all present together with one major criterion (compact-multifocal MC infiltrates in the bone marrow) and three minor criteria (aberrant expression of CD25 on MC, abnormal spindle-shaped morphology and c-KIT D816V somatic mutation) for SM. This evidence concerns the gene JAK2 and essential thrombocythemia.