New indices, Iron deficiency anemia, Thalassemia trait. Background: The two most frequent types of microcytic hypochromic anemia in developing countries are beta thalassemia trait (-TT) and iron deficiency anemia (IDA). Several indices using blood cell count parameters have been suggested to differentiate between two. Aim of study: In this study, we compared the ability of different three indices (Mentzer index, RDWI and MCI) to distinguish-TT from IDA by calculating their sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) and Youden's index values. Methods: A total of 98 carefully selected children aged 1.0-17 years were evaluated. We calculated 3 discrimination indices in all patients with hemoglobin (Hb) values of 3.8-11.7 g/dL. None of the subjects had a combined case of IDA and-TT. The patient groups were evaluated according to red blood distribution width index; the Mentzer index and Matos and Carvalho index (MCI). Results: The Mentzer index was the most reliable index, as it had the highest sensitivity (96.06%), specificity (82.98%), and Youden's index (79.04%) for detecting-TT; this was followed by the RDW index (87.23%, 86.27%, and 73.5%, resp.) and MCI (91.49%, 80.04%, and 71.53%). Conclusion: The Mentzer index provided the highest reliabilities for differentiating-TT from IDA.