This is a Phase IV, multicenter, non-interventional, non-randomized, prospective, observational study in an adult population (patients >18 years old) of men and women who have been diagnosed with clinically overt PV and are being followed in either community or academic medical centers in the United States who will be enrolled over a 12-month period and observed for 36 months from the date the last patient is enrolled.

Inclusion Criteria:

• Age ≥18 years
• Diagnosis of Polycythemia Vera (PV)
• Willing and able to provide written informed consent
• Willing and able to complete patient assessment questionnaires either alone or with minimal assistance from a caregiver and/or trained site personnel
• Under the supervision of a physician for the current care of PV including but not limited to watchful waiting, acetylsalicylic acid (ASA) 81mg or greater, antithrombotic therapy, Phlebotomy (PHL), Hydroxyurea (HU), interferon (recombinant or pegylated), busulfan, anagrelide

Exclusion Criteria:

• Participation in an active clinical trial in which the study treatment is blinded
• Life expectancy <6 months
• Diagnosis of myelofibrosis (MF) [including primary MF, post-PV MF, or post-essential thrombocythemia MF (post-ET MF)]
• Diagnosis of secondary Acute Myeloid Leukemia (AML)
• Diagnosis of Myelodysplastic Syndrome (MDS)
• History of or active plan to proceed to allogeneic hematopoietic stem cell transplant in next 3 months
• Splenectomy

An adult population (patients >18 years old) of men and women who have been diagnosed with clinically overt PV will be enrolled. Sites will include both community and academic centers across the United States that are representative of where patients with PV are diagnosed and treated.