β-Thalassemia major is an inherited blood disorder, which mainly affects the Mediterranean region. Osteoporosis represents an important cause of morbidity in β-thalassemia major and its pathogenesis has not been completely clarified. Genetic factors play an important role in the pathogenesis of osteoporosis and several candidate gene polymorphisms have been implicated in the regulation of this process. A G→T polymorphism in the regulatory region of the collagen type I alpha 1 (COLIAI) gene at a recognition site for transcription factor Sp1 has been strongly associated with osteoporosis. The aim of the present study was to examine the distribution of COLIAI polymorphism and its relationship with bone mineral density (BMD) at the lumbar spine and femur in patients and controls. In this study, the G→T polymorphism was detected in 31 Egyptian β-thalassemia major patients and 20 healthy controls and its possible association with BMD was investigated. Alleles S and s were detected by the presence of a G or T nucleotide, respectively, in a regulatory site of the COLIAI gene using polymerase chain reaction (PCR). A total of 80.6% of the β-thalassemia patients were homozygous for G/G (SS) and 19.4% were heterozygotes for G/T (Ss) polymorphism. There was no ss genotype in our patients. In the control group, 70 and 30% had SS and Ss genotypes, respectively. There was no significant difference between Z-score of patients with SS and Ss at head of femur (P = 1) or at lumbar spine (P = 0.48). Conclusion Our results raise the possibility that genotyping at the Sp1 site could be of clinical value in identifying the thalassemic patients at risk of developing osteoporosis.