The aim of this prospective longitudinal study was to measure prospectively the bone mineral density (BMD) and anthropometric variables after a hip fracture. In particular, we studied changes in the BMD in both the injured and uninjured hips, and examined if the postoperative mortality rate and complications, including pseudarthrosis of the fracture and late segmental collapse of the head of the femur, could be predicted by early bone mass measurements. The bone mineral density and the body composition were measured with dual energy X-ray absorptiometry in 102 consecutive hip fracture patients, 31 men and 71 women, with a mean age of 74 and 79 years, respectively. All cases were operated on within 3 days. The measurements were undertaken within 10 days after the fracture, after 4 and after 12 months. The BMD of the hip fracture cases decreased, especially in the lower extremities where the patients lost 7%, during the first year after the fracture. The patients also lost lean body mass (5%) but gained fat (11%) during the same period. They lost significantly more bone mass in the fractured hip than in the uninjured hip (p < 0.05). No difference was found between those patients who survived and those who died within 2 years after their hip fracture in neither the initial measurement nor in the follow-up measurements. Also, we found no difference between those patients whose hip fracture healed and those who developed late segmental collapse or pseudarthrosis. In conclusion, osteoporotic hip fracture cases lose bone mass at an increased rate, especially in the fractured hip. Also, their soft tissue composition changes, gaining fat while losing muscle mass. Furthermore, it seems that early bone mineral measurements cannot predict postoperative failures or postoperative mortality.