Polycythaemia vera (PV) is an haematological neoplasm that frequently presents neurological symptoms. However, chorea is a rare complication of this disease, occurring in less than 5% of the patients. Cognitive impairment related to PV unbalanced is also a rare complication, and it can improve with proper treatment. We present a 96-year-old-man with acute-onset hemichorea and frontal lobe syndrome with no vascular pathology in the basal ganglia or frontal region. A clear relationship was observed between the onset of involuntary movements and the cognitive impairment and worsening of haematological parameters in the patient. After causal and symptomatic treatment, the patient’s clinical status improved. In the elderly, PV must be considered as a cause of acute chorea and sudden cognitive impairment, as early diagnosis leads to effective treatment and prevention of complications.