Although the beta (beta) thalassaemia carrier frequency in Turkey was stated to be 2 per cent, the prevalence rate varies widely in different regions and there is limited data confirming the disorder in Aegean region. This prevalence study was planned to determine frequency of beta thalassaemia trait in the Aegean region among 1124 high school students, between 13 and 18 years old, who were selected as target population. Sensitivity of mean corpuscular volume (MCV) and mean corpuscular haemoglobin (MCH) in prediction of beta thalassaemia trait were evaluated. Venous blood samples were obtained for haemoglobin electrophoresis, HbA2 and HbF, serum iron and total iron binding capacity from students in whom the levels of haemoglobin (Hb), haemotocrite (Hct), MCV, or MCH, were low compared to normal values. The prevalence of beta thalassaemia trait in Aegean region was 3 per cent. Sensitivity of MCV and MCH for determining beta thalassaemia trait were 100 and 96 per cent, respectively.