We measured the quantitative ultrasound (QUS) parameters broadband ultrasound attenuation (BUA) and speed of sound (SOS) at the calcaneus using an ultrasound imaging device (UBIS 3000) in 698 healthy Caucasian male and female subjects (110 prepubertal, 356 pubertal/adolescent and 210 adult) between 6 and 77 years of age. The influence of different region of interest (ROI) diameters (6-20 mm) and software techniques (automatic (ROIaut), copied (ROIcop) and fixed coordinate (ROIfix) measurements) on annual rate of change, trend assessment interval (TAI; an estimate of the follow-up time required for measuring a true change), percentage of positioning errors (positioning of the ROI partly at the cortical edge or even partly beyond the calcaneus) and short-term precision error was studied. When using ROI diameters increasing from 8 to 20 mm, the annual rate of change of BUA and SOS did not change in adults, but was higher in prepubertal subjects (when subjects with positioning errors were excluded) as well as in pubertal/adolescent subjects. TAIs for BUA were shortest when using ROIaut with ROI diameters between 8 and 14 mm (TAI between 1.2 and 1.5 years for prepubertal boys and pubertal/adolescent subjects, 2.4 years for prepubertal girls, 2.7 years for postmenopausal women, and 9 years in men and premenopausal women). TAIs for SOS were 4 years or more, except for postmenopausal women (2.1 years) and prepubertal boys (3.2 years). Measurements with large ROI diameters, especially with fixed region coordinates, resulted in a high percentage of positioning errors and mostly in longer TAIs. Analysis of the short-term precision errors did not reveal these important differences between the various ROI diameters. Our results indicate that calcaneal ultrasound imaging may be useful for measuring skeletal changes in healthy children, especially with BUA, and in postmenopausal women with BUA and SOS using an automatic measurement in the region of lowest attenuation. ROI diameters of 12 mm should be used in prepubertal subjects and of 14 mm in pubertal/adolescent and adult subjects.