Background: Hydroxyurea (HU) is among the most commonly used cytoreductive treatments for polycythemia vera (PV), but previous research and clinical experience suggest that not all patients respond optimally, consistently, or durably to HU treatment. This study investigated patterns of HU use and impact on disease control among patients with PV in real-world clinical practice in the United States. Methods: Oncologists and hematologists recruited between April and July 2014 reported data from patient charts. Treatment history and disease symptom comparisons between HU subgroups were performed using Chi square tests or one-way analyses of variance for categorical and continuous variables. Other analyses were performed using descriptive statistics. Results: Overall, 329 physicians participated and provided data on 1309 patients with PV (62.3 % male; mean age = 62.5 years, mean time since diagnosis = 5.2 years). In the 229 (17.5 %) patients who had stopped HU, the most common reasons for HU discontinuation-as assessed by the treating clinician-were inadequate response (29.3 %), intolerance (27.5 %), and disease progression (12.7 %). Among patients currently on HU, a significant proportion had elevated blood cell counts: 34.4 % had hematocrit values >= 45 %, 59.4 % had platelet levels >400 x 10(9)/L, and 58.2 % had WBC counts >10 x 10(9)/L. Two-thirds (66.3 %) of patients had >= 1 elevated count, 40.3 % had >= 2 elevated counts, and 19.8 % had all 3 counts elevated. The most common PV-related signs and symptoms among all patients were fatigue and splenomegaly. Conclusions: Although many patients with PV benefit from HU therapy, some continue to have suboptimal control of their disease, as evidenced by persistence of abnormally elevated blood cell counts and the continued experience of disease-related manifestations (signs and symptoms). These data further denote a significant medical need for some patients with PV currently or previously treated with HU.