We report a Korean family in which the interaction of a triplicated alpha-globin locus and a heterozygous beta-thalassemia gives rise to a clinical phenotype of thalassemia intermedia. The propositus, a 36year-old woman, was evaluated because of moderately severe chronic anemia. Molecular analysis revealed heterozygosity for a single beta-thalassemia mutation, IVSII-1 (G->A). Additionally, she was found to have co-inherited a triplicated alpha-globin gene (alphaalpha/alphaalphaalphaanti3.7). In contrast, her brother heterozygous for the same triplicated alpha-locus and beta-thalassemia was clinically normal, suggesting that the delicate balance between alpha- and beta-chains is controlled by other currently not identified factors. Thalassemia intermedia due to co-inheritance of alphaalpha/alphaalphaalphaanti3.7 and IVSII-1 (G->A) was rare, and in Korea, this patient is the first case of thalassemia intermedia attributable to this combined abnormalities.