Calcitonin (CT) plays a role in the pathogenesis of osteoporosis and genetic variations in or adjacent to the CT gene may be associated with loss of bone mineral density (BMD). The correlation between a dinucleotide (cytosine-adenine) repeat polymorphism at the CT locus and BMD was examined in 70 osteoporotic women, 70 non-osteoporotic women and 500 subjects from the Mexican population. The allele A and genotype AA frequencies were significantly higher in osteoporotic women than in non-osteoporotic women (60% vs 32%; p < 0.0001 and 41% vs 14%; p = 0.0007, respectively). Genotype AA was associated with the presence of osteoporosis [odds ratio 2.58; 95% confidence interval (CI); 1.62-4.12]. Likewise, the loss of lumbar BMD and T scores were related to the presence of allele A: subjects with a single A allele displayed lower values for lumbar BMD and T score (84.02% and -1.51, respectively) than those who do not present any A allele (89.61% and -0.88, respectively). Individuals with two alleles A showed the lowest lumbar BMD and T-score values (73.77% and -2.51, respectively). Analysis of potential confounder demonstrated that aging has a significant effect on osteoporosis development (odds ratio 1.1; 95% CI; 1.1052-1.152).