Megaloblastic anemia causes macrocytic anemia from ineffective red blood cell production and intramedullary hemolysis. The most common causes are folate (vitamin B9) deficiency and cobalamin (vitamin B12) deficiency. Megaloblastic anemia can be diagnosed based on characteristic morphologic and laboratory findings. However, other benign and neoplastic diseases need to be considered, particularly in severe cases. Therapy involves treating the underlying cause-eg, with vitamin supplementation in cases of deficiency, or with discontinuation of a suspected medication.