Two brothers from a Chinese family with beta-thalassemia intermedia who harbor both alpha- and beta-globin gene defects are described. They are both compound heterozygous for codons 41/42 (-CTTT) beta0-thalassemia and nt - 28 (A > G) beta(+)-thalassemia mutations together with concurrent (- -SEA) alpha-thalassemia (SEA) deletion. One sibling also harbors Hb Westmead, giving an unusual genotype of beta0/beta(+)-thalassemia and (- -SEA) alpha-thalassemia/Hb Westmead. With respect to the age at presentation and transfusion requirement, this subject shows a milder clinical phenotype than his brother, most probably explainable by the presence of Hb Westmead in addition to the SEA deletion, which causes a further amelioration of the alpha-chain excess and hence a less severe disease. For areas with high prevalence of both alpha- and beta-thalassemia mutations, their interactions should always be considered in genotype phenotype correlation. Moreover, routine laboratory diagnostic strategy for non-deletional alpha-globin gene mutations in the Chinese may need to include Hb Westmead, as it is a common alpha-globin gene mutation in our population apart from Hb Constant Spring and Hb Quong Sze.