Postpolycythaemic myelofibrosis (PPMF) is a known complication of polycythaemia vera (PV) but information regarding its incidence and predisposing factors is not well defined. In 116 subjects consecutively diagnosed with PV in a single institution (median age 62 years, range: 20-88), the probability of PPMF was analysed by the Kaplan-Meier method, followed by the log-rank test. With a mean follow-up of 8 years (95% confidence interval: 6.6-9), 17 patients had evolved into PPMF (15%). The probability of evolution to PPMF was 16% at 10 years and 34% at 15 years. Age, gender, spleen size, leucocytosis, thrombocytosis or cytoreductive treatment were not associated with an increased risk of PPMF. The actuarial probability of PPMF at 15 years was higher in those patients presenting at diagnosis with endogenous megakaryocytic colony formation (59% when present versus 10% when absent, P = 0.03), an elevated serum lactate dehydrogenase (LDH) level (69% vs. 23% in patients with normal LDH, P = 0.04), and in those who were heterozygous for the JAK2 V617F mutation (55% vs. 17% in heterozygotes, P = 0.04). In conclusion, PPMF is a frequent complication in PV patients at 15 years with the risk being higher in patients with increased LDH, endogenous megakaryocytic colony formation or a high JAK2 V617F allele burden.