This study investigates the prevalence and degree of low bone mineral density (BMD) in a group of 108 institutionalized men with developmental disabilities. Speed of sound (SOS) and broadband attenuation (BUA) of the calcaneus were measured to determine a quantitative ultrasound index (QUI). Comparison was made to the values for this index in a reference population of age-matched and young adult controls. Thirty-four percent of the study participants had QUI values more than 2 standard deviations (SDs) below those of age-matched controls. Fifty-one percent of this population showed QUI values more than 2 SDs below those of the young adult reference group, suggesting a high prevalence of significantly decreased BMD.