To evaluate the role of local bone mineral density (BMD) in the etiology of hip fractures, we measured the hip BMD using dual photon absorptiometry in 29 females who had recently suffered a hip fracture associated with minimal or moderate, but not major, trauma and compared their BMD to those of 14 young normal females, 58 early postmenopausal normal females, 13 age-matched normal females, and 114 spinal osteoporotic females without a hip fracture. Hip-fractured patients had a BMD significantly lower (P less than 0.001) than that of all other studied groups, suggesting that a low hip BMD is associated with hip fracture risk. A femoral neck BMD below 0.75 g/cm2 suggests an increased likelihood for developing a hip fracture. Peak BMD was measured at 1.03 g/cm2, a value comparable to published normative data. Thus, a loss in hip BMD of approximately 30% from peak mineral density appears necessary before a hip fracture may occur after moderate trauma.