This study investigated prevalence and associated-factors of low quantitative ultrasound (QUS) values by screening calcaneal QUS parameters--broadband ultrasound attenuation (BUA) and speed of sound (SOS)--in population samples of three different Taiwanese communities. The study included 6,322 subjects (2,631 male and 3,691 female), aged 31 yr old or more in Shih-Pai (a metropolitan area in northern Taiwan),Yu-Chi (a mountain area in central Taiwan), and A-Lein (a seaside area in southern Taiwan). The overall response rate was 50.2%. The correlation between BUA and SOS was 0.684, p<0.001. From those who responded, we selected 403 subjects aged 31-40 yr as the reference (the young group), and their BUA was 65.34+/-7.91 dB/MHz. The t-score was calculated from the BUA data of our reference group. The percentile of -2.5<t-score<-1.0 and t-score< or =-2.5 in male subjects was 21.4 and 2.9%, respectively, and in female subjects 24.2 and 14.1%, respectively. The BUA of urban area subjects was higher than that of rural area subjects in almost all age-strata, and overweight was noted to be a protective factor. The effect of age-adjusted odds ratio (AOR) on low QUS values in females was significantly increased every 10 yr from 1.55, 5.13, 13.81, 34.29, to 38.14. This survey showed that age-related decreases in calcaneal ultrasonometry, indicating prevalence of low QUS values, were more obvious in female than male subjects. Overall 38.3% of the female Taiwanese had low QUS values, and this is approximately equivalent to the lifetime risk of fracture at the hip, spine, or distal forearm in Caucasian women. The specific t-score designation, as World Health Organization (WHO) criteria, applied to calcaneal QUS are reasonable when the reference group is selected from the same population.