The clinical relevance of prior malignancy (PM) in patients with essential thrombocythemia (ET) and polycythemia vera (PV) is largely unknown. We retrospectively evaluated 437 patients (ET, n=263; PV, n=174) treated at MD Anderson between 1960 and 2010. Forty-four patients had PM (ET, 10%; PV, 11%), with median time to diagnosis of 66 months. PM was not associated with abnormal cytogenetics, JAK2-mutation frequency, blood-cell counts or progression to acute leukemia or myelofibrosis. In multivariate analysis, only older age and high LDH levels were associated with worse OS. In conclusion, PM does not predict worse outcomes for patients with ET and PV.