This paper describes a complex combination of four thalassemia genes (delta(+), beta(0), nondeletion and deletion alpha-thalassemia) in the spouse of a typical high Hb A2 beta-thalassemia carrier presenting for genetic counselling. This complex gene combination resulted in a hematological phenotype, characterized by thalassemia-like red cell indices, normal Hb A2 and Hb F levels and slightly reduced alpha/beta globin chain synthesis ratio, and therefore not indicative for the presence of beta-thalassemia trait. Family studies in combination with alpha-globin gene mapping, haplotype analysis at the beta-globin gene cluster and definition of the beta-thalassemia mutation by oligonucleotide hybridization led us to identify a beta-thalassemia mutation, to define the molecular basis for this phenotype and give the appropriate genetic counselling.