Serum ferritin is an iron-binding protein and is the target of the most sensitive and specific tests used for the identification of iron deficiency.1,2 In recent years, serum ferritin levels <30 ng/mL were considered to indicate iron deficiency even if the hemoglobin (Hb) content was within the reference range. In clinical practice, it is recommended that individuals with serum ferritin levels <40 ng/mL are considered iron deficient.1 In the field of pediatrics and child psychiatry, reduced serum ferritin is known to be associated with sleep disorder due to restless legs syndrome (RLS),3 attention-deficit/hyperactivity disorder,4 and tic severity.5 For RLS, iron administration is recommended when serum ferritin is <50 ng/mL.3 However, few studies have focused on serum ferritin itself to investigate the effect of reduced serum ferritin on psychological and physical symptoms of children. This study evaluated psychiatric features of children with reduced serum ferritin concentration and elucidated the effect of iron administration on the psychological and physical symptoms of the children who visited outpatient clinic.