beta-Thalassemia, an inherited blood disorder, mainly affects people from the Mediterranean region. This life-threatening anemia is so severe that regular blood transfusions and iron-chelating therapy is obligatory throughout life. Commonly occurring complications, especially in adult patients, are osteopenia and osteoporosis. Osteoporotic fractures are strongly associated with bone density, which is under polygenic control. Type I collagen, which is encoded by the COLIA1 and COLIA2 genes, is the major protein in the bone. A G-->T polymorphism in the regulatory region of the COLIA1 gene at a recognition site for transcription factor Sp1 has been strongly associated with osteoporotic fractures. In this study, the G-->T polymorphism is screened in 42 beta-thalassemia major and 10 beta-thalassemia intermedia patients. 64.3% of the beta-thalassemia patients were heterozygotes for G/T (Ss) polymorphism and 35.7% were homozygous for G/G (SS), 60% of the beta-thalassemia intermedia patients were heterozygous (Ss) and 40% were homozygous (ss). The number of heterozygotes in the beta-thalassemia major group was significantly higher, compared to the control group (F = 13.615, P = 0.001). The number of heterozygotes in beta-thalassemia intermedia group was also significantly higher, compared to the control group (F = 5.158, P = 0.029). Patients who are G/T heterozygotes (Ss) at the polymorphic Sp1 site have a lower bone mineral density than G/G homozygotes (SS) (P = 0.01).