RESUMEN
Polycythemia vera (PV) is a chronic myeloproliferative disorder characterized by uncontrolled red blood cell production. Megaloblastic anemia is caused by deficiency of cobalamin (vitamin B12) and/or folate (vitamin B9). While B12 deficiency may be caused by insufficient dietary intake or impairment of its utilization, its association with PV is described without exact knowledge of the physiopathology. We herein report the occurrence of megaloblastic anemia due to Vitamin B12 deficiency in an 85-year-old North African woman patient with PV. This case highlights this atypical presentation of PV and challenges that comes with it causing the delay of diagnosis and the complexity of its diagnosis and treatment. Keywords: megaloblastic anemia, polycythemia vera, association, case report.