Aim. The aim of the present study was to examine differences in calcaneal broadband ultrasound attenuation for healthy adult men and women approaching peak bone mass and, to examine the influence of side dominance and selected lifestyle factors such as physical activity. Methods. A total of 158 men and women aged 19 to 25 years were recruited. Right and left calcaneal BUA was measured using the QUS-2 Ultrasound Densitometer (Quidel Corp, CA). Bone-specific physical activity, dietary calcium intake, smoking habits, alcohol intake, medications, menstrual history and lower limb side dominance were recorded. Results. Short-term BUA measurement precision was 1.6-2.5%. Male BUA was significantly greater than female (101.5 ᱮ9 vs. 90.4 ᱮ5 dB/MHz, P = 0.001). Although there was no main effect of age, BUA appeared to increase in men across the age range such that a non-significant sex difference at 19 became significant by age 25 (P = 0.002). There was no dominance effect on BUA for either sex. Bone-specific physical activity, height, weight, and BMI contributed to variance in male BUA, while only bone-specific physical activity and weight accounted for female BUA variation (P < 0.05). Conclusion. Young adult men have considerably greater BUA than age-matched women. BUA has largely peaked by age 19 in women but continues to increase through age 25 in men. Calcaneal BUA is positively related to body weight and participation in bone-specific physical activity in young adult men and women.