Although delta-globin gene (HBD MIM#142000) mutations have no clinical implications, co-inheritance of beta- and delta-thalassemia may lead to misdiagnosis. Among 7,153 samples studied for beta-thalassemia, 205 samples with lower than expected HbA2 levels were selected for our analysis and 183 samples (2.5%) were positive for delta-globin gene mutations. Twelve different mutations were detected, and among these five have not been not previously described (HbA2-Catania HBD c.8A-->T, HbA2-Corleone HBD c.41C-->A, HbA2-Ventimiglia HBD c.212C-->G, HbA2-Montechiaro HBD c.260C-->A, and HbA2-Bagheria HBD c.422C-->T). This study suggests that delta-globin gene defects are very common in Sicily. Thus, these mutations need to be considered during beta-thalassemia screening to avoid false negative results in the detection of at-risk couples.