Abstract Background Diagnosis and treatment of iron deficiency anemia in older subjects improves their quality of life. Serum ferritin as a marker of iron stores is an acute phase protein. In older subjects who usually have many concomitant chronic medical conditions, serum ferritin may increase in response to inflammatory processes irrespective of iron stores. This study was performed to determine the diagnostic properties of serum ferritin in the diagnosis of iron deficiency anemia in older subjects. Methods This case-control study included all the inhabitants of Amirkola town who participated in the Amirkola Health and Aging Project. Diagnosis of anemia was confirmed based on a hemoglobin level <13 g/dL in men and <12 g/dL in women and iron deficiency anemia by percent transferrin saturation <15%. A receiver operating characteristic curve was constructed to determine an optimal serum ferritin cutoff value to differentiate patients with and without iron deficiency anemia at the highest sensitivity and specificity. Results Eighty patients with iron deficiency anemia and 160 cases of anemia without iron deficiency (mean age: 72.9 ± 8 and 71.6 ± 7.6 years, respectively; p-value = 0.37) were analyzed. In iron deficiency anemia, the mean serum ferritin was significantly lower (p-value = 0.036) compared to patients without iron deficiency anemia. Serum ferritin with a cutoff level of 100 ng/mL differentiated patients with and without iron deficiency anemia with a sensitivity of 60% and specificity of 59% and area under the receiver operating characteristic curve of 0.615 ± 0.040 (95% confidence interval: 0.536-0.694; p-value = 0.004). Conclusion These findings indicate that in elderly subjects, iron deficiency anemia may develop with higher levels of serum ferritin. Hence, the conventional cutoff of serum ferritin for the diagnosis of iron deficiency anemia in young adults is not appropriate for the elderly population.