Age-related hyperkyphosis is thought to be a result of underlying vertebral fractures, but studies suggest that among the most hyperkyphotic women, only one in three have underlying radiographic vertebral fractures. Although commonly observed, there is no widely accepted definition of hyperkyphosis in older persons, and other than vertebral fracture, no major causes have been identified. To identify important correlates of kyphosis and risk factors for its progression over time, we conducted a 15-year retrospective cohort study of 1196 women, aged 65 years and older at baseline (1986 to 1988), from four communities across the United States: Baltimore County, MD; Minneapolis, MN; Portland, OR; and the Monongahela Valley, PA. Cobb angle kyphosis was measured from radiographs obtained at baseline and an average of 3.7 and 15 years later. Repeated measures, mixed effects analyses were performed. At baseline, the mean kyphosis angle was 44.7 degrees (SE = 0.4, SD = 11.9) and significant correlates included a family history of hyperkyphosis, prevalent vertebral fracture, low bone mineral density, greater body weight, degenerative disc disease, and smoking. Over an average of 15 years, the mean increase in kyphosis was 7.1 degrees (SE = 0.25). Independent determinants of greater kyphosis progression were prevalent and incident vertebral fractures, low bone mineral density and concurrent bone density loss, low body weight, and concurrent weight loss. Thus, age-related kyphosis progression may be best prevented by slowing bone density loss and avoiding weight loss.