Objectives:Deficiencies in folate (FA) and vitamin B12 (VB12) are causes of macrocytic anemia. However, in clinical practice, FA and/or VB12 deficiency can occur in patients with normocytic anemia. This study aimed to determine the prevalence of FA/VB12 deficiency in patients with normocytic anemia and the importance of vitamin replacement therapy in these patients.Methods:We retrospectively reviewed electronic medical record information of patients whose hemoglobin and serum FA/VB12 concentrations were measured at the Department of Hematology (N=1,388) and other departments (N=1,421) of Fujita Health University Hospital.Results:In the Hematology Department, 530 (38%) patients showed normocytic anemia. Of these, 49 (9.2%) had FA/VB12 deficiency. Twenty of 49 (41%) patients had some hematological malignancies and 27 (55%) had benign hematological disorders. Of the nine patients who received vitamin replacement therapy, one showed a partial improvement in the hemoglobin concentration of ≥1 g/dL.Conclusions:In the clinical setting, the measurement of FA/VB12 concentrations in patients with normocytic anemia may be useful. Replacement therapy may be a treatment option to consider in patients with low FA/VB12 concentrations. However, physicians need to pay attention to the presence of background diseases, and the mechanisms of this situation require further investigation.