Myelofibrosis (MF), polycythemia vera (PV) and essential thrombocythemia (ET) are three classic BCR ABL fusion gene-negative chronic myeloproliferative neoplasms (MPNs). Though rare, it is important to understand the burden of illness of these disorders for public health planning, healthcare insurers and pharmaceutical manufacturers. Therefore, we have described the incidence of MF and prevalence of MF, ET and PV in the United States between 2008 and 2010 based on data from two large health plans. The incidence of primary MF was about 1 per 100 000 per year and did not vary over the study years. The prevalence of PV (44–57 per 100 000) and ET (38–57 per 100 000) was much higher than that of MF (4–6 per 100 000) or subgroups containing MF (post-PV MF = 0.3–0.7 per 100 000; post-ET MF = 0.5–1.1 per 100 000). Additional research using other national databases and/or study designs is needed to substantiate these findings.