Essential thrombocythemia and Myelofibrosis and Polycythemia Vera are amongs the Philadelphia negative myeloproliferative neoplasms. Diagnosis of Chronic myelocytic leukemia by Philadelphia chromosome with 100 percent specifity is of great value for molecular test. Exon 14 mutation of JAK₂V617F and exon 12 mutation is positive in more than 95 percent of polycythemia vera cases.Jak₂V617F mutation is positive in about 50% of primary myelofibrosis and essential thrombocythemia cases. The finding of calreticulin(CALR) mutations in Jak2 negative cases of thrombocythemia and myelofibriosis seems to close the molecular diagnosis gap of Jak2 and Philadelphia negative myeloptoliferative neoplasm. The new mutation has prognostic importance of thrombosis risk and give better evaluation of peripheral smear and bone marrow.