Background/Aims: Individuals with double heterozygosity for α- and β-thalassaemia and heterozygous β-thalassaemia show a similar haematological picture. Co-inheritance of α- and β-thalassaemia in both partners may result in pregnancies with either Hb Bart’s hydrops foetalis or β-thalassaemia major, or pregnancies with both disorders. Methods: The co-inheritance of α-thalassaemia in 322 β-thalassaemia carriers in Malaysia was studied. Results: The frequency of α-thalassaemia in the β-thalassaemia carriers was 12.7% (41/322), with a carrier frequency of 7.8% for the SEA deletion, 3.7% for the -α3.7 deletion, 0.9% for Hb Constant Spring and 0.3% for the -α4.2 deletion. Conclusion: Double heterozygosity for α- and β-thalassaemia was confirmed in 5 out of the 41 couples and the risk of the fatal condition Hb Bart’s hydrops foetalis was confirmed in two of these couples. Detection of the Southeast Asian (SEA) deletion in the Malaysian Malays in this study confirms that Hb Bart’s hydrops foetalis can occur in this ethnic group. Results of this study have provided new information on the frequency and different types of α-thalassaemia (--SEA, -α3.7 and -α4.2 deletions, Hb Constant Spring) in Malaysian β-thalassaemia carriers.