BACKGROUND The concept of 'Myeloproliferative Neoplasms' (MPNs) was introduced by William Dameshek(1) in 1951 by grouping together Chronic Myeloid Leukaemia (CML), Polycythaemia Rubra Vera (PRV), Essential Thrombocythaemia (ET), Primary Myelofibrosis (PMF) and Erythroleukaemia; a self-perpetuating trilineage myeloproliferation was underlined as the pathogenesis. JAK2 is one of the 4 Janus Kinases, which are non-receptor tyrosine kinases that are integral part of the cytokine and growth factor signalling. Its autoinhibitory function is released by a gain of mutation in the JAK2 V617F mutation. It leads to downstream activation of several signalling cascades like STAT proteins, PI3K-AKT pathway and mitogen activated protein kinases. Recent studies suggest that mutations in the TET2 tumour suppressor gene, which have been found in 17% of JAK2 V617F+ Ph-MPNs and 7% of JAK2V617Ecases, likely precede the acquisition of the JAK2 V617F mutation. Detection of mutation can be by Direct sequencing, Restriction fragment length polymorphism or allele-specific PCR. JAK2 Exon 12 Mutation is specific to JAK2 V617F negative PRV73. JAK2 N542E543 deletion is the most frequent among the ones described. These patients are usually heterozygous for the mutation with Erythroid myelopoiesis, subnormal serum erythropoietin levels and younger age at diagnosis. Apart from BCR-ABL mutation, others include JAK2 V617E, JAK2 EXON12, MPL, KIT, Calreticulin and TET2 mutations. The Objectives of our Study were 1. To study the clinico-morphologic features of Myeloproliferative Neoplasms with reference to the 2008 revised WHO classification of myeloid neoplasms. 2. To study the prevalence of JAK2 V617E in our region. MATERIALS AND METHODS It will be a descriptive study that is set in the Haematology Clinical Pathology Laboratory of MCH, Thiruvananthapuram. The bone marrow samples that are obtained from the Department of Medicine, which show features of MPNs are selected (based on the revised criteria). For these selected cases, the clinical history is collected and is compared with the peripheral smear, bone marrow aspirate, trephine and reticulin stain and the MPN is typed. JAK2 V617E study is advised for the cases of PRV. RESULTS A total of 60 Myeloproliferative Neoplasms were studied with a male predominance (63.2%) and the most frequent age group being 40 -80 years. Most were cases of Polycythaemia Rubra Vera (35%) followed by Essential Thrombocythaemia (30%), Chronic Myeloid Leukaemia and Progressive Myelofibrosis (15%), Chronic Neutrophilic Leukaemia and Chronic Eosinophilic Leukaemia. Most cases were incidentally detected and a statistically significant relationship was noted between presenting complaint and the type of MPN. The cases of MPN were studied for JAK2 mutation status as well, showed 24% positivity with 9.5% cases being lost to followup. Among the JAK2 positive cases, 60% presented with thrombotic episodes and 60% had splenomegaly. CONCLUSION 60 cases of MPN were studied; cases selected in accordance with the 2008 WHO classification of myeloid neoplasms. Polycythaemia Rubra Vera is the commonest. Cases of PRV, ET, CIMF, CNL and CEL are being identified with more frequency compared to the earlier study conducted in our Department in 1994, probably because of increased awareness of these conditions and also better and clearcut diagnostic criteria available.