The emergency providers generally encounters myeloproliferative disorders (MPNs) in 1 of 2 ways: as striking laboratory abnormalities of seeming unknown consequence, or in previously diagnosed patients presenting with complications. The course of patients with MPNs is highly variable, but major complications can arise. Emergent conditions related to hyperviscosity need to be recognized early and treated aggressively. Rapid hydration, transfusion, cytoreduction, and early hematology consultation can be lifesaving. Likewise, although management is not altered, a high index of suspicion for thrombotic complications is required in patients with known MPNs as these are a significant cause of morbidity and mortality.