Bone density predicts the risk of hip fracture. Because hip strength is determined by bone geometry and architecture as well as density, we tested which variables in geometry and architecture were independent discriminators of hip fracture and, if combined with density, improved the discrimination of fracture from non-fracture over bone density alone. The design was a case-control study. The subjects were Caucasian women over the age of 60 years who had sustained a hip fracture after the age of 58 years (n = 22), and controls matched for age and weight (n = 43) and unmatched controls (n = 317) with no history of hip fracture. Variables in density, geometry and architecture were obtained from dual-energy X-ray absorptiometry images and from radiographs of the upper end of the femur. In a univariate model, of the measures of bone mass, the best discriminator of hip fracture was bone mineral density of the neck of femur; of the geometric measurements, it was hip axis length; and of the measurements of bone architecture, it was Singh grade. In a multivariate model, these three variables were shown to be independent discriminators of hip fracture. When hip axis length was combined with bone mineral density, there was significant improvement in discrimination of hip fracture (p = 0.014), and when Singh grade was combined with hip axis length and bone mineral density there was a further significant improvement (p = 0.002).(ABSTRACT TRUNCATED AT 250 WORDS)