Iron deficiency is the most common micronutrient deficiency among Indian preschool children contributing to increased burden of morbidity and mortality and the most significant negative consequence of iron deficiency is iron deficiency anemia (IDA). Recent NFHS–III surveys (2005–06) have shown that 70-85% (approx. 79.2%) of Indian young children have anemia [
1]. IDA is attributed to inadequate iron intake, poor bioavailability of iron or high nutritional needs during childhood which is further exacerbated by chronic intestinal blood losses due to helminth infections and in many areas due to severe malarial infections [
2,
3]. Studies have shown that iron deficiency causes delay in cognitive development and poor motor and sensory system functioning and that iron supplementation in early years may prevent these complications among children [
4]. Conversely, there is an evidence suggesting that routine iron treatment in non-iron deficient children may have adverse consequences for morbidity and infections [
5,
6]. Therefore, it is very important to detect iron deficiency (ID) at its earliest stage in children especially in a low resource setting and replenish the iron stores by proper supplementation, thereby preventing many of the adverse developmental and behavioral effects caused by IDA. Currently, the detection of IDA is largely dependent upon quantification of biochemical markers like serum ferritin (SFr), serum transferrin (STr) and zinc protoporphyrin (ZnPP) which are not routinely available and affordable in developing countries due to high costs. Moreover, these tests are altered by inflammation, which limits their applicability for clinical interpretation, especially in areas with high infection rates. Another limitation of the commonly used hematological tests is their poor sensitivity or specificity as they can be modified by conditions other than iron deficiency. Studies have shown that RDW in addition to other hematological markers like mean corpuscular volume (MCV) and hemoglobin can be used as a differential diagnostic tool for identification of iron deficiency anemia [
7‐
9]. Various studies also show that the onset of iron deficiency anemia can be predicted using automated blood analyzers [
7], as a low haemoglobin level along with a high level of anisocytosis detectable by red cell distribution width prove to be good indicators of changes in blood due to depleted iron stores [
8]. It seems that the earliest hematological manifestation of iron deficiency is marked by an elevated level of RDW [
9] and reports have shown that it is a cost-effective screening tool for early diagnosis of IDA in comparison to SFr and ZnPP [
9‐
11]. The red blood cell (RBC) distribution width, a measure of variations in the width of circulating RBCs, reported as a part of complete blood count [
12] has been known to be of value in the discrimination of iron deficiency anemia from other causes of microcytic anemia, but studies in pediatric populations are lacking. Thus, in the present study we evaluated the discriminative ability of RDW diagnostic test for detecting iron deficiency anemia among children aged 1–3 yrs in a low socio-economic setting using receiver’s operating characteristic curve (ROC) analyses.