Although δ-globin gene (HBD MIM#142000) mutations have no immediate physical consequence, it can interfere with the diagnosis of β-thalassemia (β-thal), which can be severe. In the present study, of 40,863 samples referred for thalassemia trait screening, 167 samples with lower than expected Hb A(2) levels, in the presence or absence of a second Hb A(2) fraction, were selected for our analysis and 152 samples (0.4%) were positive for δ-globin gene mutations. Twenty-one different mutations were detected, and of these 12 have not been previously described. We found that -77 (T>C) was the most common mutation in Chinese followed by -30 (T>C), together accounting for almost 82.3% of the total number of δ-globin gene defects. Since compound heterozygotes for β-thal and a δ-globin gene mutation may have low mean cell volume (MCV) and normal Hb A(2) levels, and therefore be overlooked as β-thal heterozygotes, a detailed molecular analysis for both α- and β-thal is necessary, especially when one partner has been identified to have β-thal trait.