Beta-thalassemia is the most common disease among hemoglobinopathies in Antalya, Turkey, as well as worldwide. Mutations found in Turkish beta- thalassemia patients constitute a heterogeneous group, consisting mostly of point mutations. Only in very rare cases did deletions or insertions cause affected or carrier phenotypes. Hb Knossos [beta 27 (B9) Ala-Ser] is a rare variant with a normal HbA2 level. In this study, we aimed to investigate the effect of compound heterozygosity for Hb Knossos [Cod 27 (G-T)] and IVSII-745 (CG). To our knowledge, this is the first report of such a combination related with beta- thalassemia major phenotype in a Turkish family, where reverse dot blot hybridization (RDBH) and DNA sequencing analysis were used. Heterozygous inheritance of the mutation results in mild beta-thalassemia phenotype, whereas homozygous inheritance leads to intermediate beta-thalassemia. As a result, the compound heterozygosity of Hb Knossos with IVSII-745 appears as the cause of the beta-thalassemia major phenotype in our case. The combination of these mutations [Hb Knossos, Cod 27 (G-T), and IVSII-745, C-G] causes the beta-thalassemia major phenotype, and this is important for genetic counseling.