Previous studies have demonstrated that an Sp1 binding site polymorphism in the collagen type I gene (COLIA1) is related to reduced bone mineral density (BMD) and osteoporotic fractures in certain populations, particularly in the elderly. We have examined the relationship among these COLIA1 Sp1 alleles, BMD, quantitative ultrasound properties of bone, and fractures in a population-based cohort of elderly women from the UK. The study group comprised 314 women aged 75 years and over who agreed to participate in a clinical study of bisphosphonate therapy in preventing bone loss at the hip. Women were enrolled regardless of the presence or absence of osteoporosis, but those with other diseases that might affect skeletal metabolism were excluded. The genotype distribution for the Sp1 polymorphism was in Hardy-Weinberg equilibrium (SS - 78%; Ss - 20%; ss - 2%) but the proportion of individuals who carried the "s" allele (22%) was significantly lower than previously observed in another study of the UK population (37.1%) (P < 0.001). There were no significant associations between COLIA1 genotypes and metacarpal cortical index, BMD of the forearm, tibial SOS, calcaneal SOS, or calcaneal BUA. While there was a trend towards lower BMD values at the hip in patients with Ss and ss genotypes, this was not statistically significant (SS = 0.721 +/- 0.14; Ss = 0.704 +/- 0.13; ss = 0.683 +/- 0.20 P = 0.6). Prevalent vertebral fractures occurred in 22% of subjects and prior fractures of the wrist, ankle, and hip were reported by 20%, but there was no significant difference in COLIA1 genotype distribution between fracture patients and controls. We conclude that COLIA1 Sp1 alleles are not significantly associated with BMD, ultrasound properties of bone, or fractures in this population-based sample of elderly women.