Polymorphisms at the binding site of the Sp 1 transcription factor of the collagen type I alpha1 gene have recently been suggested to be an important marker for low bone mineral density (BMD) and vertebral fracture in a population of predominantly postmenopausal British women. We examined whether the unfavorable "s" allele was associated with low BMD in 64 patients with primary osteoporosis and in 72 healthy controls. We found no statistically significant differences between COLIA1 genotypes with regard to BMD at the spine and femoral neck. In 36 patients with severe osteoporosis with vertebral fracture the genotype frequencies were similar to that observed in 67 age-matched controls. These data indicate that the Sp 1 polymorphisms in the COLIA1 gene are unlikely to be of clinical value in identifying Swedish subjects who are at risk of postmenopausal osteoporosis.