Introduction: Polycythemia Vera (PV) is a chronic myeloproliferative neoplasia generatingan accumulation of erythrocytes in the peripheral blood (polyglobulia). Reportedprevalence is close to 2 cases per 100 thousand inhabitants/year worldwide. The disease is described as polysymptomatic but with unspecificmanifestations, such as plethora, itching and splenomegaly. Thus, a diagnosis of polycythemia is usually suspected when it is found in casual blood tests and suchfinding cannot be explained by secondary causes. Psychiatric symptoms have been described for the disease, mostly in papersfrom the beginning of the 20th century, but are rare in current clinical practice. Case report: Male patient, 54 years old, was admitted to the emergency room withpsychiatric symptoms which started one month prior. An organic origin wassuspected, due to the patient's age and healthy condition, and was hospitalized forclinical control and investigation. Investigation showed polycythemia and on the thirdday of hospitalization, he was discharged with psychiatric medication. After four days, the patient returned with the same symptoms. He wastransferred to another hospital, where he was discharged with more psychiatricdrugs. He maintained an outpatient follow-up with the psychiatric team, oligosymptomatic, reducing the dose of medications. Six months after the second hospitalization, the patient was taken to thehospital again and new tests were requested. Due to hyperviscosity a phlebotomywas performed. After four phlebotomies and reintroduction of psychiatric medication, there was an improvement in the symptoms and laboratory stabilization, and thepatient was discharged. He started an follow-up with hematology and psychiatry. The patient gatheredcriterias for starting PV treatment with hydroxyurea and phlebotomies, leading to acomplete improvement of the condition. The psychiatric team suspended themedications after one year due to adverse reactions to the treatment and absence ofsymptoms. Discussion: Initial studies from the 1920's described the diseases as variablesymptomatology with mainly neurologic and eventually psychiatric symptoms. Reports of such symptoms became more scarce as the years went by. Thepopularization of hemograms, allowing for earlier diagnosis, and more effectivetreatment protocols may have contributed for a reduction of complicated cases, making the psychiatric symptoms rarer. When they appear, psychiatric symptoms are referred as being resistant topsychiatric treatment but responsive to the hematological one. Literature shows thatthese symptoms remain uncontrolled with the use of antipsychotics, but disappearwith cytoreduction even without the usage of psychiatric drugs. Conclusion: The case stands out for its exceptionality: psychiatric and neurological manifestations are rare and were already considered such in older studies. Despitethis, the case behaved consistently with the literature. The patient had polyglobuliasince the onset of the condition, was refractory to psychiatric treatment, even havingside effects from it, and was responsive to hematological treatment. Lastly, the case warns of the importance of cautious and complete analysis of complementary exams. As this did not happen, the patient stayed a greater periodwith uncontrolled mental status and increased thromboembolic risk, the main causeof death in these patients.