The variability of bone mass and bone strength is in part genetically determined. The pathophysiology of the disease is complex and its heritability is almost certainly polygenic. In a large group of women from north eastern Italy, homogeneous for calcium intake and other risk factors for osteoporosis, we investigated three different genetic polymorphic markers that have been associated with bone mineral density (BMD). The study includes 663 postmenopausal (aged 48-85 years) and 52 perimenopausal (aged 47-53 years) women. Lumbar spine and hip BMD were measured by dual energy X-ray absorptiometry (DXA). After DNA extraction, the restriction enzymes utilized were MscI for the SP1 site of the collagen type I regulatory region (COLIA1), AluI for the calcitonin receptor (CTR) gene, and BsmI for the Vitamin D receptor (VDR) gene. COLIA1 genotype was significantly associated with age-adjusted hip BMD, with the highest values in the SS group and the lowest in the ss group (p < 0.05). The COLIA1 effect was not visible until the sixth decade of life, but it increased thereafter with aging, becoming statistically significant also at the lumbar spine in subjects aged >70 years. CTR genotype was also significantly related to bone mass in the CC group, with the lowest age and weight-adjusted BMD values at the spine (p < 0.05). The CTR genotype effect was greater in the younger subset of women. This suggests that the CTR genotype might influence the process of acquiring peak bone mass rather than the process of bone loss along aging. No trend association was found between BMD values and VDR genotype. These findings suggest an association between the COLIA1 gene polymorphism more with the age-related rate of bone loss than with peak bone mass, which apparently is somewhat affected by CTR gene polymorphism.