The classical Philadelphia chromosome-negative myeloproliferative neoplasms (MPN) comprise the clinically and pathologically related polycythemia vera (PV), essential thrombocythemia (ET) and primary myelofibrosis (PMF). The diagnosis, classification and therapeutic stratification of these disorders is multifactorial and dependent upon clinical presentation, peripheral blood and bone marrow morphological features, hematological and other laboratory parameters, and increasingly, the underlying genetic signature.