Background: -Thalassemias are a heterogeneous group of autosomal disorders caused by inherited mutations that decrease the synthesis of α and β globin chains of hemoglobin causing varying degree of anemia. They are among the most common genetic disorders worldwide with a prevalence of thalassemia carriers being 1.5-7%. Symptoms vary from silent, asymptomatic carriers to transfusion dependent anemia. Aim of the study: - To evaluate the diagnostic usefulness of complete blood count using various red cell parameters in detection of thalassemia trait in microcytic hypochromic anemia cases. Material and methods: - All samples received in central laboratory for CBC were analyzed for Hb, RBC count, MCV, MCH, MCHC and RDW. A total of 550 cases were selected based on criterion of Hb < 12 g /dl , MCV < 80 fl and RDW(CV)- < 18%. All the samples were sent for HbA2 estimation by HPLC. Results: -Out of 550 microcytic hypochromic cases, 397 were diagnosed with microcytic hypochromic anemia with normal HPLC pattern, whereas 153 cases were diagnosed with β thalassemia trait with HPLC A2 value more than 3.8. In our study, the incidence of beta thalassemia trait came out to be approx. 27.8 % in microcytic hypochromic cases. Conclusion:- CBC is a very simple and cheap technique with high predictive value in screening of beta thalassemia trait in microcytic hypochromic anemia. It can be used for mass screening where Thalassemia prevalence is high.