The prevalence of osteoporosis and factors associated with treatment initiation after detection of osteoporosis were determined for previously unscreened, postmenopausal women. Dual-energy x-ray absorptiometry screening was conducted in 1997-2000 as part of an ancillary study of the Buffalo, New York, center of the Women's Health Initiative Observational Study. A total of 945 women were previously unaware of their bone density, although, for 344 (36.4%), osteoporosis was newly detected through screening (T-score </= -2.5). Of those women, 250 (72.7%) discussed the results with a health care provider, and 140 (56.0%) initiated treatment after doing so. In multivariate logistic regression analyses, factors associated with treatment initiation were T-score (odds ratio (OR) = 0.39 per unit increase, 95% confidence interval (CI): 0.23, 0.67), routine medical care more often than yearly (OR = 2.08, 95% CI: 1.12, 3.86), college education (OR = 2.58, 95% CI: 1.25, 5.31), family income of >/=$50,000 (OR = 2.06, 95% CI: 1.03, 4.14), and discussing screening results with a gynecologist (OR = 3.20, 95% CI: 1.33, 7.67). These findings suggest that many postmenopausal women are unaware of their bone density and could benefit from screening. In this study, approximately half of the women with osteoporosis initiated treatment after screening. Disease severity, medical care frequency, education, income, and physician type predicted treatment initiation.