We have undertaken a large population screening study to identify the molecular basis of hemoglobinopathies in the central Greece region. A total of 845 unrelated beta-thalassemia patients and alpha-, beta-, and deltabeta-thalassemia carriers have been recruited and screened for mutations in the alpha- and beta-globin gene clusters. The alpha(-MED) deletion and the Turkish inversion/deletion are the most frequent genetic rearrangements leading to alpha- and deltabeta-thalassemia respectively, contrary to the situation in the rest of the country, while the beta -101 (C>T) promoter mutation is surprisingly frequent in the central part of Greece. Our data indicate that determination of mutation frequencies in different regions is vital for accurate provision of genetic services and counseling and for precise estimation of genetic diversity.