A study of the spectrum of b-Thalasimia mutations in the West Bank revealed the presence of ten different b-globin mutations. The study involved 42 patients with B-thal major and 43 suspected carriers with Cooley’s anemia. The IVS1.6 mutation predominated with a frequency of 52.8% and was almost invariably associated with chromosome haplotype VI. Seven other mutations (-30, FS5, IVS1.1, IVS1.110, N37, N39, IVS2.1), commonly found in the Mediterranean basin, occurred with frequency of 0.8% to 11.0%. In addition +G insertion in FS8/9 and N15 (a lesion previously found in Asian Indians and rarely found in the Mediterranean population) was demonstrated in two patients with haplotype I. The IVS1.6 homozygous patients were variable in their need for transfusion from dependent to independent phenotype. Characterization of the IVS1.6 variable phenotype is under way and may reveal further mutation in the b-globin cluster or other genetic modification.