Abstract: The present study reports the results in 284 patients of applying a recently developed index, MCV - (10xRBC), for discrimination between beta-thalassemia trait (β-TT) and Iron Deficiency Anemia (IDA), the two most common causes of microcytic hypochromic anemias. A total of 284 carefully selected patients (130 patients with IDA and 154 with β-TT) were studied. Sensitivity, specificity and Youden’s index were compared between the proposed index and four other indices, namely England-Fraser, Mentzer, Srivastava and RBC count. The new index correctly identified 263 (92.96%) patients, standing inferior only to Mentzer which correctly diagnosed 269 (94.71%) patients. The best discrimination index according to Youden’s criteria was Mentzer (Youden’s index = 90.1) followed by the new index (Youden’s index = 85.5). There are remarkable inconsistencies among the results obtained in different studies. Larger studies are needed to establish the optimal discrimination index as well as to confirm the results obtained in the present study. Nevertheless, the epidemiological indices of the proposed discrimination index and the simplicity of its calculation make it acceptable for use in Iran.