Iron deficiency anemia (IDA) and megaloblastic anemia due to vitamin B12 deficiency are well-characterized prototypes of anemia. There is no doubt that IDA is the most common hematologic disorder in Korea and worldwide as well. The diagnosis and treatment of IDA is not a difficult practice usually, however, a caution is required in detecting early-stage iron deficiency and in distinguishing IDA from anemia of chronic disorders such as chronic inflammatory disease, malignancies, chronic liver disease, and chronic renal disease. Administration of a standard iron preparation at a proper dosage over an adequate period is a prerequisite for the successful treatment of IDA, which is sometimes overlooked by both physicians and patients. Early detection and treatment as well as prevention of iron deficiency per se are also required. Pernicious anemia is the most common cause of vitamin B₁₂ deficiency in Western populations. By contrast, the disorder is rare in Korea, although the number of cases seems to be increasing these days. The majority of patients with megaloblastic anemia reveal a history of gastrectomy. Thus, it should be reminded that vitamin B₁₂ supplementation is important to prevent the development of overt deficiency or anemia in these susceptible individuals, since a delay in the treatment of vitamin B₁₂ deficiency may result in an irreversible neurologic deficit.