Background: Beta thalassemia is a common health problem in Iran especially in Northern provinces. Premarital screening for thalassemia is compulsory in Iran and identification of the carriers is based on primary CBC (Cell Blood Count) and hemoglobin electrophoresis. Silent mutations on β-globin gene have borderline or normal hematological indices that cannot be detected in premarital screening.
Material and Methods: A 4 years old boy affected with β-thalassemia was referred to the lab for molecular analysis. During the screening program for β-thalassemia, his father and mother were diagnosed as α and β-thalassemia carrier respectively. 
Results: The results of molecular analysis showed that in addition to the α-globin single gene deletion (α^3.7) the father have also carried a silent mutation on his β-globin gene named HBB c.82G>T or Hb ^Knossos that was missed in screening program.
Conclusion: The presented case shows that using CBC and hemoglobin electrophoresis in premarital screening program for detecting β-thalassemia carriers is not a valid approach and individuals who are carriers of silent β-globin gene mutations are missed in this procedure. Hence, in premarital screening program precise molecular investigation especially when the partner is a typical β-thalassemia carrier is recommended.