Myeloproliferative neoplasms (MPNs) are clonal hematopoietic stem cell disorders with shared gene mutations, excess blood production and wide range of clinicopathological changes. JAK2, CALR and MPL gene mutation study has become one of the major criteria in the diagnosis of MPNs. This study focused on the common laboratory findings in patients with genetically proven MPNs at age 50 and younger with clinical correlation and follow up. There were 54 patients in this study, including 36 essential thrombocythemia (66.7%), 13 polycythemia vera (24.1%), 2 primary myelofibrosis (3.7%) and 3 MPN-unclassifiable (5.5%). The male/female ratio was 1/2 in patients with essential thrombocythemia, and about 1/1 in patients with other types of MPNs. Thrombocytosis and abnormal megakaryocytic proliferation were the most common findings in peripheral blood and bone marrow biopsy specimens, 88.9% and 96.8% respectively. Thrombotic event was recorded more often in patients with polycythemia vera than essential thrombocythemia, 30.1% and 19.4% respectively. Myelofibrosis, evolving acute myeloid leukemia and disease related mortality were seen only in patients with polycythemia vera, but not in patients with essential thrombocythemia. The findings in this study suggested that genetically induced abnormal megakaryocytic proliferation might play a critical role in the early pathogenesis of MPNs. With an increased risk for thrombotic event and disease progression, patients with polycythemia vera may need more follow up evaluation and therapeutic intervention than those with essential thrombocythemia. Anti-megakaryocytic therapy may be a future direction in the management of young MPN patients.