The purpose of this prospective study was to monitor the bone mineral density (BMD) of the lumbar spine and contralateral femoral neck in the first year following an osteoporosis-related fracture of the hip. Eighty-three elderly patients (mean age 77 years) who had sustained a hip fracture had determinations of BMD made at the time of fracture; 49 of these patients were available for reassessment of BMD 1 year later. The change in BMD was correlated with pre- and postinjury variables, such as ambulatory ability, dietary intake of calcium, serum vitamin D levels, mental status, and routine serologies. The mean decrease in BMD in the year following fracture was 5.4% from the contralateral femoral neck and 2.4% from the lumbar spine. Calcium intake correlated with the loss of BMD from the femoral neck (p = 0.015), but not the lumbar spine. Patients with daily calcium intakes of less than 500 mg/day had a more than 10% decrease in femoral neck BMD in the year following their hip fracture. Serum 1,25-dihydroxy vitamin D level correlated with loss of MBD from the lumbar spine (p = 0.001), but not from the femoral neck. There was no correlation between the loss of bone mineral from either measurement site and age, sex, level of ambulation, or mental status. The loss of BMD from the femoral neck in the year following a hip fracture is more than five times that reported in the nonfractured population. This accelerated rate of loss can have drastic consequences in an elderly population already exhibiting osteopenia and propensity to fall. Investigation of pharmacologic or other interventions in the first critical year following a hip fracture may potentially blunt this accelerated rate of bone loss and lessen the risk of subsequent fractures.